| Message ID | 20231205-qcom_stats-aeabi_uldivmod-fix-v1-1-f94ecec5e894@quicinc.com |
|---|---|
| State | New |
| Headers | show |
| Series | soc: qcom: stats: Fix division issue on 32-bit platforms | expand |
On Wed, Dec 06, 2023 at 02:07:16PM +0000, David Laight wrote: > From: Bjorn Andersson > > Sent: 06 December 2023 00:44 > > > > commit 'e84e61bdb97c ("soc: qcom: stats: Add DDR sleep stats")' made it > > in with a mult_frac() which causes link errors on Arm and PowerPC > > builds: > > > > ERROR: modpost: "__aeabi_uldivmod" [drivers/soc/qcom/qcom_stats.ko] undefined! > > > > Expand the mult_frac() to avoid this problem. > > > > Fixes: e84e61bdb97c ("soc: qcom: stats: Add DDR sleep stats") > > Reported-by: Randy Dunlap <rdunlap@infradead.org> > > Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com> > > --- > > drivers/soc/qcom/qcom_stats.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/soc/qcom/qcom_stats.c b/drivers/soc/qcom/qcom_stats.c > > index 4763d62a8cb0..5ba61232313e 100644 > > --- a/drivers/soc/qcom/qcom_stats.c > > +++ b/drivers/soc/qcom/qcom_stats.c > > @@ -221,7 +221,8 @@ static int qcom_ddr_stats_show(struct seq_file *s, void *unused) > > > > for (i = 0; i < ddr.entry_count; i++) { > > /* Convert the period to ms */ > > - entry[i].dur = mult_frac(MSEC_PER_SEC, entry[i].dur, ARCH_TIMER_FREQ); > > + entry[i].dur *= MSEC_PER_SEC; > > + entry[i].dur = div_u64(entry[i].dur, ARCH_TIMER_FREQ); > > Is that right? > At a guess mult_frac(a, b, c) is doing a 32x32 multiply and then a 64x32 > divide to generate a 32bit result. > So I'd guess entry[i].dur is 32bit? (this code isn't in -rc4 ...). > Which means you are now discarding the high bits. > entry[i].dur is 64 bit, so this should work just fine. Arnd proposed that as ARCH_TIMER_FREQ is evenly divisible by MSEC_PER_SEC we just div_u64(dur, ARCH_TIMER_FREQ / MSEC_PER_SEC), and I picked that patch instead. > You've also added a very slow 64bit divide. Without checking the generated code, I'd expect this to be a slow 64-bit division already. But this is a debug function, so it should be fine to take that penalty. > A multiple by reciprocal calculation will be much better. > Since absolute accuracy almost certainly doesn't matter here convert: > dur * 1000 / FREQ > to > (dur * (u32)(1000ull << 32 / FREQ)) >> 32 > which will be fine provided FREQ >= 1000 > I'm quite sure you're right regarding the accuracy. I think as this isn't in a hot path, the more readable div_u64() feels like a reasonable choice. Thank you for your input and suggestion though! Regards, Bjorn > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales)
diff --git a/drivers/soc/qcom/qcom_stats.c b/drivers/soc/qcom/qcom_stats.c index 4763d62a8cb0..5ba61232313e 100644 --- a/drivers/soc/qcom/qcom_stats.c +++ b/drivers/soc/qcom/qcom_stats.c @@ -221,7 +221,8 @@ static int qcom_ddr_stats_show(struct seq_file *s, void *unused) for (i = 0; i < ddr.entry_count; i++) { /* Convert the period to ms */ - entry[i].dur = mult_frac(MSEC_PER_SEC, entry[i].dur, ARCH_TIMER_FREQ); + entry[i].dur *= MSEC_PER_SEC; + entry[i].dur = div_u64(entry[i].dur, ARCH_TIMER_FREQ); } for (i = 0; i < ddr.entry_count; i++)
commit 'e84e61bdb97c ("soc: qcom: stats: Add DDR sleep stats")' made it in with a mult_frac() which causes link errors on Arm and PowerPC builds: ERROR: modpost: "__aeabi_uldivmod" [drivers/soc/qcom/qcom_stats.ko] undefined! Expand the mult_frac() to avoid this problem. Fixes: e84e61bdb97c ("soc: qcom: stats: Add DDR sleep stats") Reported-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com> --- drivers/soc/qcom/qcom_stats.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- base-commit: adcad44bd1c73a5264bff525e334e2f6fc01bb9b change-id: 20231205-qcom_stats-aeabi_uldivmod-fix-4a63c7ec013f Best regards,