| Message ID | 20231003122251.3325435-7-adhemerval.zanella@linaro.org |
|---|---|
| State | Accepted |
| Commit | 03bf8357e8291857a435afcc3048e0b697b6cc04 |
| Headers | show |
| Series | Use introsort for qsort | expand |
On Tue, Oct 3, 2023 at 7:23 AM Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote: > > This patch removes the mergesort optimization on qsort implementation > and uses the introsort instead. The mergesort implementation has some > issues: > > - It is as-safe only for certain types sizes (if total size is less > than 1 KB with large element sizes also forcing memory allocation) > which contradicts the function documentation. Although not required > by the C standard, it is preferable and doable to have an O(1) space > implementation. > > - The malloc for certain element size and element number adds > arbitrary latency (might even be worse if malloc is interposed). > > - To avoid trigger swap from memory allocation the implementation > relies on system information that might be virtualized (for instance > VMs with overcommit memory) which might lead to potentially use of > swap even if system advertise more memory than actually has. The > check also have the downside of issuing syscalls where none is > expected (although only once per execution). > > - The mergesort is suboptimal on an already sorted array (BZ#21719). > > The introsort implementation is already optimized to use constant extra > space (due to the limit of total number of elements from maximum VM > size) and thus can be used to avoid the malloc usage issues. > > Resulting performance is slower due the usage of qsort, specially in the > worst-case scenario (partialy or sorted arrays) and due the fact > mergesort uses a slight improved swap operations. > > This change also renders the BZ#21719 fix unrequired (since it is meant > to fix the sorted input performance degradation for mergesort). The > manual is also updated to indicate the function is now async-cancel > safe. > > Checked on x86_64-linux-gnu. > --- > include/stdlib.h | 2 - > manual/argp.texi | 2 +- > manual/locale.texi | 3 +- > manual/search.texi | 7 +- > stdlib/Makefile | 2 - > stdlib/msort.c | 309 --------------------------------------------- > stdlib/qsort.c | 14 +- > 7 files changed, 16 insertions(+), 323 deletions(-) > delete mode 100644 stdlib/msort.c > > diff --git a/include/stdlib.h b/include/stdlib.h > index 0ed8271d9b..580da9be15 100644 > --- a/include/stdlib.h > +++ b/include/stdlib.h > @@ -149,8 +149,6 @@ extern int __posix_openpt (int __oflag) attribute_hidden; > extern int __add_to_environ (const char *name, const char *value, > const char *combines, int replace) > attribute_hidden; > -extern void _quicksort (void *const pbase, size_t total_elems, > - size_t size, __compar_d_fn_t cmp, void *arg); > > extern int __on_exit (void (*__func) (int __status, void *__arg), void *__arg); > > diff --git a/manual/argp.texi b/manual/argp.texi > index 0023441812..b77ad68285 100644 > --- a/manual/argp.texi > +++ b/manual/argp.texi > @@ -735,7 +735,7 @@ for options, bad phase of the moon, etc. > @c hol_set_group ok > @c hol_find_entry ok > @c hol_sort @mtslocale @acucorrupt > -@c qsort dup @acucorrupt > +@c qsort dup > @c hol_entry_qcmp @mtslocale > @c hol_entry_cmp @mtslocale > @c group_cmp ok > diff --git a/manual/locale.texi b/manual/locale.texi > index 720e0ca952..f6afa5dc44 100644 > --- a/manual/locale.texi > +++ b/manual/locale.texi > @@ -253,7 +253,7 @@ The symbols in this section are defined in the header file @file{locale.h}. > @c calculate_head_size ok > @c __munmap ok > @c compute_hashval ok > -@c qsort dup @acucorrupt > +@c qsort dup > @c rangecmp ok > @c malloc @ascuheap @acsmem > @c strdup @ascuheap @acsmem > @@ -275,7 +275,6 @@ The symbols in this section are defined in the header file @file{locale.h}. > @c realloc @ascuheap @acsmem > @c realloc @ascuheap @acsmem > @c fclose @ascuheap @asulock @acsmem @acsfd @aculock > -@c qsort @ascuheap @acsmem > @c alias_compare dup > @c libc_lock_unlock @aculock > @c _nl_explode_name @ascuheap @acsmem > diff --git a/manual/search.texi b/manual/search.texi > index 5691bf2f2b..a550858478 100644 > --- a/manual/search.texi > +++ b/manual/search.texi > @@ -159,7 +159,7 @@ To sort an array using an arbitrary comparison function, use the > > @deftypefun void qsort (void *@var{array}, size_t @var{count}, size_t @var{size}, comparison_fn_t @var{compare}) > @standards{ISO, stdlib.h} > -@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@acucorrupt{}}} > +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} > The @code{qsort} function sorts the array @var{array}. The array > contains @var{count} elements, each of which is of size @var{size}. > > @@ -199,9 +199,8 @@ Functions}): > The @code{qsort} function derives its name from the fact that it was > originally implemented using the ``quick sort'' algorithm. > > -The implementation of @code{qsort} in this library might not be an > -in-place sort and might thereby use an extra amount of memory to store > -the array. > +The implementation of @code{qsort} in this library is an in-place sort > +and uses a constant extra space (allocated on the stack). > @end deftypefun > > @node Search/Sort Example > diff --git a/stdlib/Makefile b/stdlib/Makefile > index 25e42a77e7..095518eef4 100644 > --- a/stdlib/Makefile > +++ b/stdlib/Makefile > @@ -96,7 +96,6 @@ routines := \ > mbtowc \ > mrand48 \ > mrand48_r \ > - msort \ > nrand48 \ > nrand48_r \ > old_atexit \ > @@ -380,7 +379,6 @@ generated += \ > # generated > > CFLAGS-bsearch.c += $(uses-callbacks) > -CFLAGS-msort.c += $(uses-callbacks) > CFLAGS-qsort.c += $(uses-callbacks) > CFLAGS-system.c += -fexceptions > CFLAGS-system.os = -fomit-frame-pointer > diff --git a/stdlib/msort.c b/stdlib/msort.c > deleted file mode 100644 > index bbaa5e9f82..0000000000 > --- a/stdlib/msort.c > +++ /dev/null > @@ -1,309 +0,0 @@ > -/* An alternative to qsort, with an identical interface. > - This file is part of the GNU C Library. > - Copyright (C) 1992-2023 Free Software Foundation, Inc. > - > - The GNU C Library is free software; you can redistribute it and/or > - modify it under the terms of the GNU Lesser General Public > - License as published by the Free Software Foundation; either > - version 2.1 of the License, or (at your option) any later version. > - > - The GNU C Library is distributed in the hope that it will be useful, > - but WITHOUT ANY WARRANTY; without even the implied warranty of > - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > - Lesser General Public License for more details. > - > - You should have received a copy of the GNU Lesser General Public > - License along with the GNU C Library; if not, see > - <https://www.gnu.org/licenses/>. */ > - > -#include <alloca.h> > -#include <stdint.h> > -#include <stdlib.h> > -#include <string.h> > -#include <unistd.h> > -#include <memcopy.h> > -#include <errno.h> > -#include <atomic.h> > - > -struct msort_param > -{ > - size_t s; > - size_t var; > - __compar_d_fn_t cmp; > - void *arg; > - char *t; > -}; > -static void msort_with_tmp (const struct msort_param *p, void *b, size_t n); > - > -static void > -msort_with_tmp (const struct msort_param *p, void *b, size_t n) > -{ > - char *b1, *b2; > - size_t n1, n2; > - > - if (n <= 1) > - return; > - > - n1 = n / 2; > - n2 = n - n1; > - b1 = b; > - b2 = (char *) b + (n1 * p->s); > - > - msort_with_tmp (p, b1, n1); > - msort_with_tmp (p, b2, n2); > - > - char *tmp = p->t; > - const size_t s = p->s; > - __compar_d_fn_t cmp = p->cmp; > - void *arg = p->arg; > - switch (p->var) > - { > - case 0: > - while (n1 > 0 && n2 > 0) > - { > - if ((*cmp) (b1, b2, arg) <= 0) > - { > - *(uint32_t *) tmp = *(uint32_t *) b1; > - b1 += sizeof (uint32_t); > - --n1; > - } > - else > - { > - *(uint32_t *) tmp = *(uint32_t *) b2; > - b2 += sizeof (uint32_t); > - --n2; > - } > - tmp += sizeof (uint32_t); > - } > - break; > - case 1: > - while (n1 > 0 && n2 > 0) > - { > - if ((*cmp) (b1, b2, arg) <= 0) > - { > - *(uint64_t *) tmp = *(uint64_t *) b1; > - b1 += sizeof (uint64_t); > - --n1; > - } > - else > - { > - *(uint64_t *) tmp = *(uint64_t *) b2; > - b2 += sizeof (uint64_t); > - --n2; > - } > - tmp += sizeof (uint64_t); > - } > - break; > - case 2: > - while (n1 > 0 && n2 > 0) > - { > - unsigned long *tmpl = (unsigned long *) tmp; > - unsigned long *bl; > - > - tmp += s; > - if ((*cmp) (b1, b2, arg) <= 0) > - { > - bl = (unsigned long *) b1; > - b1 += s; > - --n1; > - } > - else > - { > - bl = (unsigned long *) b2; > - b2 += s; > - --n2; > - } > - while (tmpl < (unsigned long *) tmp) > - *tmpl++ = *bl++; > - } > - break; > - case 3: > - while (n1 > 0 && n2 > 0) > - { > - if ((*cmp) (*(const void **) b1, *(const void **) b2, arg) <= 0) > - { > - *(void **) tmp = *(void **) b1; > - b1 += sizeof (void *); > - --n1; > - } > - else > - { > - *(void **) tmp = *(void **) b2; > - b2 += sizeof (void *); > - --n2; > - } > - tmp += sizeof (void *); > - } > - break; > - default: > - while (n1 > 0 && n2 > 0) > - { > - if ((*cmp) (b1, b2, arg) <= 0) > - { > - tmp = (char *) __mempcpy (tmp, b1, s); > - b1 += s; > - --n1; > - } > - else > - { > - tmp = (char *) __mempcpy (tmp, b2, s); > - b2 += s; > - --n2; > - } > - } > - break; > - } > - > - if (n1 > 0) > - memcpy (tmp, b1, n1 * s); > - memcpy (b, p->t, (n - n2) * s); > -} > - > - > -void > -__qsort_r (void *b, size_t n, size_t s, __compar_d_fn_t cmp, void *arg) > -{ > - size_t size = n * s; > - char *tmp = NULL; > - struct msort_param p; > - > - /* For large object sizes use indirect sorting. */ > - if (s > 32) > - size = 2 * n * sizeof (void *) + s; > - > - if (size < 1024) > - /* The temporary array is small, so put it on the stack. */ > - p.t = __alloca (size); > - else > - { > - /* We should avoid allocating too much memory since this might > - have to be backed up by swap space. */ > - static long int phys_pages; > - static int pagesize; > - > - if (pagesize == 0) > - { > - phys_pages = __sysconf (_SC_PHYS_PAGES); > - > - if (phys_pages == -1) > - /* Error while determining the memory size. So let's > - assume there is enough memory. Otherwise the > - implementer should provide a complete implementation of > - the `sysconf' function. */ > - phys_pages = (long int) (~0ul >> 1); > - > - /* The following determines that we will never use more than > - a quarter of the physical memory. */ > - phys_pages /= 4; > - > - /* Make sure phys_pages is written to memory. */ > - atomic_write_barrier (); > - > - pagesize = __sysconf (_SC_PAGESIZE); > - } > - > - /* Just a comment here. We cannot compute > - phys_pages * pagesize > - and compare the needed amount of memory against this value. > - The problem is that some systems might have more physical > - memory then can be represented with a `size_t' value (when > - measured in bytes. */ > - > - /* If the memory requirements are too high don't allocate memory. */ > - if (size / pagesize > (size_t) phys_pages) > - { > - _quicksort (b, n, s, cmp, arg); > - return; > - } > - > - /* It's somewhat large, so malloc it. */ > - int save = errno; > - tmp = malloc (size); > - __set_errno (save); > - if (tmp == NULL) > - { > - /* Couldn't get space, so use the slower algorithm > - that doesn't need a temporary array. */ > - _quicksort (b, n, s, cmp, arg); > - return; > - } > - p.t = tmp; > - } > - > - p.s = s; > - p.var = 4; > - p.cmp = cmp; > - p.arg = arg; > - > - if (s > 32) > - { > - /* Indirect sorting. */ > - char *ip = (char *) b; > - void **tp = (void **) (p.t + n * sizeof (void *)); > - void **t = tp; > - void *tmp_storage = (void *) (tp + n); > - > - while ((void *) t < tmp_storage) > - { > - *t++ = ip; > - ip += s; > - } > - p.s = sizeof (void *); > - p.var = 3; > - msort_with_tmp (&p, p.t + n * sizeof (void *), n); > - > - /* tp[0] .. tp[n - 1] is now sorted, copy around entries of > - the original array. Knuth vol. 3 (2nd ed.) exercise 5.2-10. */ > - char *kp; > - size_t i; > - for (i = 0, ip = (char *) b; i < n; i++, ip += s) > - if ((kp = tp[i]) != ip) > - { > - size_t j = i; > - char *jp = ip; > - memcpy (tmp_storage, ip, s); > - > - do > - { > - size_t k = (kp - (char *) b) / s; > - tp[j] = jp; > - memcpy (jp, kp, s); > - j = k; > - jp = kp; > - kp = tp[k]; > - } > - while (kp != ip); > - > - tp[j] = jp; > - memcpy (jp, tmp_storage, s); > - } > - } > - else > - { > - if ((s & (sizeof (uint32_t) - 1)) == 0 > - && ((uintptr_t) b) % __alignof__ (uint32_t) == 0) > - { > - if (s == sizeof (uint32_t)) > - p.var = 0; > - else if (s == sizeof (uint64_t) > - && ((uintptr_t) b) % __alignof__ (uint64_t) == 0) > - p.var = 1; > - else if ((s & (sizeof (unsigned long) - 1)) == 0 > - && ((uintptr_t) b) > - % __alignof__ (unsigned long) == 0) > - p.var = 2; > - } > - msort_with_tmp (&p, b, n); > - } > - free (tmp); > -} > -libc_hidden_def (__qsort_r) > -weak_alias (__qsort_r, qsort_r) > - > - > -void > -qsort (void *b, size_t n, size_t s, __compar_fn_t cmp) > -{ > - return __qsort_r (b, n, s, (__compar_d_fn_t) cmp, NULL); > -} > -libc_hidden_def (qsort) > diff --git a/stdlib/qsort.c b/stdlib/qsort.c > index d5f205affc..fd32a165e7 100644 > --- a/stdlib/qsort.c > +++ b/stdlib/qsort.c > @@ -19,7 +19,6 @@ > Engineering a sort function; Jon Bentley and M. Douglas McIlroy; > Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993. */ > > -#include <alloca.h> > #include <limits.h> > #include <memswap.h> > #include <stdlib.h> > @@ -265,8 +264,8 @@ insertion_sort_qsort_partitions (void *const pbase, size_t total_elems, > stack size is needed (actually O(1) in this case)! */ > > void > -_quicksort (void *const pbase, size_t total_elems, size_t size, > - __compar_d_fn_t cmp, void *arg) > +__qsort_r (void *const pbase, size_t total_elems, size_t size, > + __compar_d_fn_t cmp, void *arg) > { > char *base_ptr = (char *) pbase; > > @@ -398,3 +397,12 @@ _quicksort (void *const pbase, size_t total_elems, size_t size, > insertion_sort_qsort_partitions (pbase, total_elems, size, swap_type, cmp, > arg); > } > +libc_hidden_def (__qsort_r) > +weak_alias (__qsort_r, qsort_r) > + > +void > +qsort (void *b, size_t n, size_t s, __compar_fn_t cmp) > +{ > + return __qsort_r (b, n, s, (__compar_d_fn_t) cmp, NULL); > +} > +libc_hidden_def (qsort) > -- > 2.34.1 > LGTM Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
diff --git a/include/stdlib.h b/include/stdlib.h index 0ed8271d9b..580da9be15 100644 --- a/include/stdlib.h +++ b/include/stdlib.h @@ -149,8 +149,6 @@ extern int __posix_openpt (int __oflag) attribute_hidden; extern int __add_to_environ (const char *name, const char *value, const char *combines, int replace) attribute_hidden; -extern void _quicksort (void *const pbase, size_t total_elems, - size_t size, __compar_d_fn_t cmp, void *arg); extern int __on_exit (void (*__func) (int __status, void *__arg), void *__arg); diff --git a/manual/argp.texi b/manual/argp.texi index 0023441812..b77ad68285 100644 --- a/manual/argp.texi +++ b/manual/argp.texi @@ -735,7 +735,7 @@ for options, bad phase of the moon, etc. @c hol_set_group ok @c hol_find_entry ok @c hol_sort @mtslocale @acucorrupt -@c qsort dup @acucorrupt +@c qsort dup @c hol_entry_qcmp @mtslocale @c hol_entry_cmp @mtslocale @c group_cmp ok diff --git a/manual/locale.texi b/manual/locale.texi index 720e0ca952..f6afa5dc44 100644 --- a/manual/locale.texi +++ b/manual/locale.texi @@ -253,7 +253,7 @@ The symbols in this section are defined in the header file @file{locale.h}. @c calculate_head_size ok @c __munmap ok @c compute_hashval ok -@c qsort dup @acucorrupt +@c qsort dup @c rangecmp ok @c malloc @ascuheap @acsmem @c strdup @ascuheap @acsmem @@ -275,7 +275,6 @@ The symbols in this section are defined in the header file @file{locale.h}. @c realloc @ascuheap @acsmem @c realloc @ascuheap @acsmem @c fclose @ascuheap @asulock @acsmem @acsfd @aculock -@c qsort @ascuheap @acsmem @c alias_compare dup @c libc_lock_unlock @aculock @c _nl_explode_name @ascuheap @acsmem diff --git a/manual/search.texi b/manual/search.texi index 5691bf2f2b..a550858478 100644 --- a/manual/search.texi +++ b/manual/search.texi @@ -159,7 +159,7 @@ To sort an array using an arbitrary comparison function, use the @deftypefun void qsort (void *@var{array}, size_t @var{count}, size_t @var{size}, comparison_fn_t @var{compare}) @standards{ISO, stdlib.h} -@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@acucorrupt{}}} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} The @code{qsort} function sorts the array @var{array}. The array contains @var{count} elements, each of which is of size @var{size}. @@ -199,9 +199,8 @@ Functions}): The @code{qsort} function derives its name from the fact that it was originally implemented using the ``quick sort'' algorithm. -The implementation of @code{qsort} in this library might not be an -in-place sort and might thereby use an extra amount of memory to store -the array. +The implementation of @code{qsort} in this library is an in-place sort +and uses a constant extra space (allocated on the stack). @end deftypefun @node Search/Sort Example diff --git a/stdlib/Makefile b/stdlib/Makefile index 25e42a77e7..095518eef4 100644 --- a/stdlib/Makefile +++ b/stdlib/Makefile @@ -96,7 +96,6 @@ routines := \ mbtowc \ mrand48 \ mrand48_r \ - msort \ nrand48 \ nrand48_r \ old_atexit \ @@ -380,7 +379,6 @@ generated += \ # generated CFLAGS-bsearch.c += $(uses-callbacks) -CFLAGS-msort.c += $(uses-callbacks) CFLAGS-qsort.c += $(uses-callbacks) CFLAGS-system.c += -fexceptions CFLAGS-system.os = -fomit-frame-pointer diff --git a/stdlib/msort.c b/stdlib/msort.c deleted file mode 100644 index bbaa5e9f82..0000000000 --- a/stdlib/msort.c +++ /dev/null @@ -1,309 +0,0 @@ -/* An alternative to qsort, with an identical interface. - This file is part of the GNU C Library. - Copyright (C) 1992-2023 Free Software Foundation, Inc. - - The GNU C Library is free software; you can redistribute it and/or - modify it under the terms of the GNU Lesser General Public - License as published by the Free Software Foundation; either - version 2.1 of the License, or (at your option) any later version. - - The GNU C Library is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU - Lesser General Public License for more details. - - You should have received a copy of the GNU Lesser General Public - License along with the GNU C Library; if not, see - <https://www.gnu.org/licenses/>. */ - -#include <alloca.h> -#include <stdint.h> -#include <stdlib.h> -#include <string.h> -#include <unistd.h> -#include <memcopy.h> -#include <errno.h> -#include <atomic.h> - -struct msort_param -{ - size_t s; - size_t var; - __compar_d_fn_t cmp; - void *arg; - char *t; -}; -static void msort_with_tmp (const struct msort_param *p, void *b, size_t n); - -static void -msort_with_tmp (const struct msort_param *p, void *b, size_t n) -{ - char *b1, *b2; - size_t n1, n2; - - if (n <= 1) - return; - - n1 = n / 2; - n2 = n - n1; - b1 = b; - b2 = (char *) b + (n1 * p->s); - - msort_with_tmp (p, b1, n1); - msort_with_tmp (p, b2, n2); - - char *tmp = p->t; - const size_t s = p->s; - __compar_d_fn_t cmp = p->cmp; - void *arg = p->arg; - switch (p->var) - { - case 0: - while (n1 > 0 && n2 > 0) - { - if ((*cmp) (b1, b2, arg) <= 0) - { - *(uint32_t *) tmp = *(uint32_t *) b1; - b1 += sizeof (uint32_t); - --n1; - } - else - { - *(uint32_t *) tmp = *(uint32_t *) b2; - b2 += sizeof (uint32_t); - --n2; - } - tmp += sizeof (uint32_t); - } - break; - case 1: - while (n1 > 0 && n2 > 0) - { - if ((*cmp) (b1, b2, arg) <= 0) - { - *(uint64_t *) tmp = *(uint64_t *) b1; - b1 += sizeof (uint64_t); - --n1; - } - else - { - *(uint64_t *) tmp = *(uint64_t *) b2; - b2 += sizeof (uint64_t); - --n2; - } - tmp += sizeof (uint64_t); - } - break; - case 2: - while (n1 > 0 && n2 > 0) - { - unsigned long *tmpl = (unsigned long *) tmp; - unsigned long *bl; - - tmp += s; - if ((*cmp) (b1, b2, arg) <= 0) - { - bl = (unsigned long *) b1; - b1 += s; - --n1; - } - else - { - bl = (unsigned long *) b2; - b2 += s; - --n2; - } - while (tmpl < (unsigned long *) tmp) - *tmpl++ = *bl++; - } - break; - case 3: - while (n1 > 0 && n2 > 0) - { - if ((*cmp) (*(const void **) b1, *(const void **) b2, arg) <= 0) - { - *(void **) tmp = *(void **) b1; - b1 += sizeof (void *); - --n1; - } - else - { - *(void **) tmp = *(void **) b2; - b2 += sizeof (void *); - --n2; - } - tmp += sizeof (void *); - } - break; - default: - while (n1 > 0 && n2 > 0) - { - if ((*cmp) (b1, b2, arg) <= 0) - { - tmp = (char *) __mempcpy (tmp, b1, s); - b1 += s; - --n1; - } - else - { - tmp = (char *) __mempcpy (tmp, b2, s); - b2 += s; - --n2; - } - } - break; - } - - if (n1 > 0) - memcpy (tmp, b1, n1 * s); - memcpy (b, p->t, (n - n2) * s); -} - - -void -__qsort_r (void *b, size_t n, size_t s, __compar_d_fn_t cmp, void *arg) -{ - size_t size = n * s; - char *tmp = NULL; - struct msort_param p; - - /* For large object sizes use indirect sorting. */ - if (s > 32) - size = 2 * n * sizeof (void *) + s; - - if (size < 1024) - /* The temporary array is small, so put it on the stack. */ - p.t = __alloca (size); - else - { - /* We should avoid allocating too much memory since this might - have to be backed up by swap space. */ - static long int phys_pages; - static int pagesize; - - if (pagesize == 0) - { - phys_pages = __sysconf (_SC_PHYS_PAGES); - - if (phys_pages == -1) - /* Error while determining the memory size. So let's - assume there is enough memory. Otherwise the - implementer should provide a complete implementation of - the `sysconf' function. */ - phys_pages = (long int) (~0ul >> 1); - - /* The following determines that we will never use more than - a quarter of the physical memory. */ - phys_pages /= 4; - - /* Make sure phys_pages is written to memory. */ - atomic_write_barrier (); - - pagesize = __sysconf (_SC_PAGESIZE); - } - - /* Just a comment here. We cannot compute - phys_pages * pagesize - and compare the needed amount of memory against this value. - The problem is that some systems might have more physical - memory then can be represented with a `size_t' value (when - measured in bytes. */ - - /* If the memory requirements are too high don't allocate memory. */ - if (size / pagesize > (size_t) phys_pages) - { - _quicksort (b, n, s, cmp, arg); - return; - } - - /* It's somewhat large, so malloc it. */ - int save = errno; - tmp = malloc (size); - __set_errno (save); - if (tmp == NULL) - { - /* Couldn't get space, so use the slower algorithm - that doesn't need a temporary array. */ - _quicksort (b, n, s, cmp, arg); - return; - } - p.t = tmp; - } - - p.s = s; - p.var = 4; - p.cmp = cmp; - p.arg = arg; - - if (s > 32) - { - /* Indirect sorting. */ - char *ip = (char *) b; - void **tp = (void **) (p.t + n * sizeof (void *)); - void **t = tp; - void *tmp_storage = (void *) (tp + n); - - while ((void *) t < tmp_storage) - { - *t++ = ip; - ip += s; - } - p.s = sizeof (void *); - p.var = 3; - msort_with_tmp (&p, p.t + n * sizeof (void *), n); - - /* tp[0] .. tp[n - 1] is now sorted, copy around entries of - the original array. Knuth vol. 3 (2nd ed.) exercise 5.2-10. */ - char *kp; - size_t i; - for (i = 0, ip = (char *) b; i < n; i++, ip += s) - if ((kp = tp[i]) != ip) - { - size_t j = i; - char *jp = ip; - memcpy (tmp_storage, ip, s); - - do - { - size_t k = (kp - (char *) b) / s; - tp[j] = jp; - memcpy (jp, kp, s); - j = k; - jp = kp; - kp = tp[k]; - } - while (kp != ip); - - tp[j] = jp; - memcpy (jp, tmp_storage, s); - } - } - else - { - if ((s & (sizeof (uint32_t) - 1)) == 0 - && ((uintptr_t) b) % __alignof__ (uint32_t) == 0) - { - if (s == sizeof (uint32_t)) - p.var = 0; - else if (s == sizeof (uint64_t) - && ((uintptr_t) b) % __alignof__ (uint64_t) == 0) - p.var = 1; - else if ((s & (sizeof (unsigned long) - 1)) == 0 - && ((uintptr_t) b) - % __alignof__ (unsigned long) == 0) - p.var = 2; - } - msort_with_tmp (&p, b, n); - } - free (tmp); -} -libc_hidden_def (__qsort_r) -weak_alias (__qsort_r, qsort_r) - - -void -qsort (void *b, size_t n, size_t s, __compar_fn_t cmp) -{ - return __qsort_r (b, n, s, (__compar_d_fn_t) cmp, NULL); -} -libc_hidden_def (qsort) diff --git a/stdlib/qsort.c b/stdlib/qsort.c index d5f205affc..fd32a165e7 100644 --- a/stdlib/qsort.c +++ b/stdlib/qsort.c @@ -19,7 +19,6 @@ Engineering a sort function; Jon Bentley and M. Douglas McIlroy; Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993. */ -#include <alloca.h> #include <limits.h> #include <memswap.h> #include <stdlib.h> @@ -265,8 +264,8 @@ insertion_sort_qsort_partitions (void *const pbase, size_t total_elems, stack size is needed (actually O(1) in this case)! */ void -_quicksort (void *const pbase, size_t total_elems, size_t size, - __compar_d_fn_t cmp, void *arg) +__qsort_r (void *const pbase, size_t total_elems, size_t size, + __compar_d_fn_t cmp, void *arg) { char *base_ptr = (char *) pbase; @@ -398,3 +397,12 @@ _quicksort (void *const pbase, size_t total_elems, size_t size, insertion_sort_qsort_partitions (pbase, total_elems, size, swap_type, cmp, arg); } +libc_hidden_def (__qsort_r) +weak_alias (__qsort_r, qsort_r) + +void +qsort (void *b, size_t n, size_t s, __compar_fn_t cmp) +{ + return __qsort_r (b, n, s, (__compar_d_fn_t) cmp, NULL); +} +libc_hidden_def (qsort)
This patch removes the mergesort optimization on qsort implementation and uses the introsort instead. The mergesort implementation has some issues: - It is as-safe only for certain types sizes (if total size is less than 1 KB with large element sizes also forcing memory allocation) which contradicts the function documentation. Although not required by the C standard, it is preferable and doable to have an O(1) space implementation. - The malloc for certain element size and element number adds arbitrary latency (might even be worse if malloc is interposed). - To avoid trigger swap from memory allocation the implementation relies on system information that might be virtualized (for instance VMs with overcommit memory) which might lead to potentially use of swap even if system advertise more memory than actually has. The check also have the downside of issuing syscalls where none is expected (although only once per execution). - The mergesort is suboptimal on an already sorted array (BZ#21719). The introsort implementation is already optimized to use constant extra space (due to the limit of total number of elements from maximum VM size) and thus can be used to avoid the malloc usage issues. Resulting performance is slower due the usage of qsort, specially in the worst-case scenario (partialy or sorted arrays) and due the fact mergesort uses a slight improved swap operations. This change also renders the BZ#21719 fix unrequired (since it is meant to fix the sorted input performance degradation for mergesort). The manual is also updated to indicate the function is now async-cancel safe. Checked on x86_64-linux-gnu. --- include/stdlib.h | 2 - manual/argp.texi | 2 +- manual/locale.texi | 3 +- manual/search.texi | 7 +- stdlib/Makefile | 2 - stdlib/msort.c | 309 --------------------------------------------- stdlib/qsort.c | 14 +- 7 files changed, 16 insertions(+), 323 deletions(-) delete mode 100644 stdlib/msort.c