| Message ID | c5765cf69bf222757463ba2653ac760b42b785e6.1527745258.git.baolin.wang@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] dma-coherent: Add one parameter to save available coherent memory | expand |
On 31/05/18 06:55, Baolin Wang wrote: > It is incorrect to use mem->size to valid if there are enough coherent > memory to allocate in __dma_alloc_from_coherent(), since some devices > may mark some occupied coherent memory by dma_mark_declared_memory_occupied(). > > So we can introduce one 'avail' parameter to save the available device > coherent memory, to valid if we have enough coherent memory for the device > to allocate. We already have dma_mem->size stored for other reasons, so there's little harm in using it for a rough sanity check to short-circuit the odd allocation which cannot possibly succeed, but adding machinery purely for the sake an ever-so-slightly more accurate, but still far from exhaustive, check doesn't really seem worth it. Even if size <= dma_mem->avail there's still no guarantee that the allocation will actually succeed, so what benefit does the explicit accounting provide? Robin. > Signed-off-by: Baolin Wang <baolin.wang@linaro.org> > --- > drivers/base/dma-coherent.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c > index 597d408..ce19832 100644 > --- a/drivers/base/dma-coherent.c > +++ b/drivers/base/dma-coherent.c > @@ -18,6 +18,7 @@ struct dma_coherent_mem { > unsigned long *bitmap; > spinlock_t spinlock; > bool use_dev_dma_pfn_offset; > + int avail; > }; > > static struct dma_coherent_mem *dma_coherent_default_memory __ro_after_init; > @@ -73,6 +74,7 @@ static int dma_init_coherent_memory( > dma_mem->device_base = device_addr; > dma_mem->pfn_base = PFN_DOWN(phys_addr); > dma_mem->size = pages; > + dma_mem->avail = pages; > dma_mem->flags = flags; > spin_lock_init(&dma_mem->spinlock); > > @@ -141,6 +143,7 @@ void *dma_mark_declared_memory_occupied(struct device *dev, > dma_addr_t device_addr, size_t size) > { > struct dma_coherent_mem *mem = dev->dma_mem; > + int order = get_order(size); > unsigned long flags; > int pos, err; > > @@ -151,7 +154,9 @@ void *dma_mark_declared_memory_occupied(struct device *dev, > > spin_lock_irqsave(&mem->spinlock, flags); > pos = PFN_DOWN(device_addr - dma_get_device_base(dev, mem)); > - err = bitmap_allocate_region(mem->bitmap, pos, get_order(size)); > + err = bitmap_allocate_region(mem->bitmap, pos, order); > + if (!err) > + mem->avail -= 1 << order; > spin_unlock_irqrestore(&mem->spinlock, flags); > > if (err != 0) > @@ -170,7 +175,7 @@ static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem, > > spin_lock_irqsave(&mem->spinlock, flags); > > - if (unlikely(size > (mem->size << PAGE_SHIFT))) > + if (unlikely(size > (mem->avail << PAGE_SHIFT))) > goto err; > > pageno = bitmap_find_free_region(mem->bitmap, mem->size, order); > @@ -182,6 +187,7 @@ static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem, > */ > *dma_handle = mem->device_base + (pageno << PAGE_SHIFT); > ret = mem->virt_base + (pageno << PAGE_SHIFT); > + mem->avail -= 1 << order; > spin_unlock_irqrestore(&mem->spinlock, flags); > memset(ret, 0, size); > return ret; > @@ -244,6 +250,7 @@ static int __dma_release_from_coherent(struct dma_coherent_mem *mem, > > spin_lock_irqsave(&mem->spinlock, flags); > bitmap_release_region(mem->bitmap, page, order); > + mem->avail += 1 << order; > spin_unlock_irqrestore(&mem->spinlock, flags); > return 1; > } >
On 1 June 2018 at 01:25, Robin Murphy <robin.murphy@arm.com> wrote: > On 31/05/18 06:55, Baolin Wang wrote: >> >> It is incorrect to use mem->size to valid if there are enough coherent >> memory to allocate in __dma_alloc_from_coherent(), since some devices >> may mark some occupied coherent memory by >> dma_mark_declared_memory_occupied(). >> >> So we can introduce one 'avail' parameter to save the available device >> coherent memory, to valid if we have enough coherent memory for the device >> to allocate. > > > We already have dma_mem->size stored for other reasons, so there's little > harm in using it for a rough sanity check to short-circuit the odd > allocation which cannot possibly succeed, but adding machinery purely for > the sake an ever-so-slightly more accurate, but still far from exhaustive, > check doesn't really seem worth it. > > Even if size <= dma_mem->avail there's still no guarantee that the > allocation will actually succeed, so what benefit does the explicit > accounting provide? > Yes, it can not guarantee one successful allocation, but it can avoid some redundant bitmap operation and reducing the preempt-disable time if we have not enough memory by checking the actual available coherent memory. By the way, I think we should also add check in dma_mark_declared_memory_occupied() and __dma_mmap_from_coherent(). -- Baolin.wang Best Regards
diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c index 597d408..ce19832 100644 --- a/drivers/base/dma-coherent.c +++ b/drivers/base/dma-coherent.c @@ -18,6 +18,7 @@ struct dma_coherent_mem { unsigned long *bitmap; spinlock_t spinlock; bool use_dev_dma_pfn_offset; + int avail; }; static struct dma_coherent_mem *dma_coherent_default_memory __ro_after_init; @@ -73,6 +74,7 @@ static int dma_init_coherent_memory( dma_mem->device_base = device_addr; dma_mem->pfn_base = PFN_DOWN(phys_addr); dma_mem->size = pages; + dma_mem->avail = pages; dma_mem->flags = flags; spin_lock_init(&dma_mem->spinlock); @@ -141,6 +143,7 @@ void *dma_mark_declared_memory_occupied(struct device *dev, dma_addr_t device_addr, size_t size) { struct dma_coherent_mem *mem = dev->dma_mem; + int order = get_order(size); unsigned long flags; int pos, err; @@ -151,7 +154,9 @@ void *dma_mark_declared_memory_occupied(struct device *dev, spin_lock_irqsave(&mem->spinlock, flags); pos = PFN_DOWN(device_addr - dma_get_device_base(dev, mem)); - err = bitmap_allocate_region(mem->bitmap, pos, get_order(size)); + err = bitmap_allocate_region(mem->bitmap, pos, order); + if (!err) + mem->avail -= 1 << order; spin_unlock_irqrestore(&mem->spinlock, flags); if (err != 0) @@ -170,7 +175,7 @@ static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem, spin_lock_irqsave(&mem->spinlock, flags); - if (unlikely(size > (mem->size << PAGE_SHIFT))) + if (unlikely(size > (mem->avail << PAGE_SHIFT))) goto err; pageno = bitmap_find_free_region(mem->bitmap, mem->size, order); @@ -182,6 +187,7 @@ static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem, */ *dma_handle = mem->device_base + (pageno << PAGE_SHIFT); ret = mem->virt_base + (pageno << PAGE_SHIFT); + mem->avail -= 1 << order; spin_unlock_irqrestore(&mem->spinlock, flags); memset(ret, 0, size); return ret; @@ -244,6 +250,7 @@ static int __dma_release_from_coherent(struct dma_coherent_mem *mem, spin_lock_irqsave(&mem->spinlock, flags); bitmap_release_region(mem->bitmap, page, order); + mem->avail += 1 << order; spin_unlock_irqrestore(&mem->spinlock, flags); return 1; }
It is incorrect to use mem->size to valid if there are enough coherent memory to allocate in __dma_alloc_from_coherent(), since some devices may mark some occupied coherent memory by dma_mark_declared_memory_occupied(). So we can introduce one 'avail' parameter to save the available device coherent memory, to valid if we have enough coherent memory for the device to allocate. Signed-off-by: Baolin Wang <baolin.wang@linaro.org> --- drivers/base/dma-coherent.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) -- 1.7.9.5