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 <[email protected]>
Signed-off-by: Bjorn Andersson <[email protected]>
---
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);
}
for (i = 0; i < ddr.entry_count; i++)
---
base-commit: adcad44bd1c73a5264bff525e334e2f6fc01bb9b
change-id: 20231205-qcom_stats-aeabi_uldivmod-fix-4a63c7ec013f
Best regards,
--
Bjorn Andersson <[email protected]>
On 12/5/23 16:44, Bjorn Andersson wrote:
> 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 <[email protected]>
> Signed-off-by: Bjorn Andersson <[email protected]>
That works. Thanks.
Acked-by: Randy Dunlap <[email protected]>
Tested-by: Randy Dunlap <[email protected]> # build-tested
> ---
> 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);
> }
>
> for (i = 0; i < ddr.entry_count; i++)
>
> ---
> base-commit: adcad44bd1c73a5264bff525e334e2f6fc01bb9b
> change-id: 20231205-qcom_stats-aeabi_uldivmod-fix-4a63c7ec013f
>
> Best regards,
--
~Randy
On 12/6/23 01:44, Bjorn Andersson wrote:
> 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 <[email protected]>
> Signed-off-by: Bjorn Andersson <[email protected]>
> ---
Thanks, I keep believeing mult_frac is generic enough to work
on something else than arm64..
Reviewed-by: Konrad Dybcio <[email protected]>
Konrad
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 <[email protected]>
> Signed-off-by: Bjorn Andersson <[email protected]>
> ---
> 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.
You've also added a very slow 64bit divide.
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
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
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 <[email protected]>
> > Signed-off-by: Bjorn Andersson <[email protected]>
> > ---
> > 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)