| Message ID | 1598969293-29228-1-git-send-email-ego@linux.vnet.ibm.com |
|---|---|
| State | New |
| Headers | show |
| Series | cpuidle-pseries: Fix CEDE latency conversion from tb to us | expand |
Hello Joel, On Wed, Sep 02, 2020 at 01:08:35AM +0000, Joel Stanley wrote: > On Tue, 1 Sep 2020 at 14:09, Gautham R. Shenoy <ego@linux.vnet.ibm.com> wrote: > > > > From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> > > > > commit d947fb4c965c ("cpuidle: pseries: Fixup exit latency for > > CEDE(0)") sets the exit latency of CEDE(0) based on the latency values > > of the Extended CEDE states advertised by the platform. The values > > advertised by the platform are in timebase ticks. However the cpuidle > > framework requires the latency values in microseconds. > > > > If the tb-ticks value advertised by the platform correspond to a value > > smaller than 1us, during the conversion from tb-ticks to microseconds, > > in the current code, the result becomes zero. This is incorrect as it > > puts a CEDE state on par with the snooze state. > > > > This patch fixes this by rounding up the result obtained while > > converting the latency value from tb-ticks to microseconds. > > > > Fixes: commit d947fb4c965c ("cpuidle: pseries: Fixup exit latency for > > CEDE(0)") > > > > Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> > > Reviewed-by: Joel Stanley <joel@jms.id.au> > Thanks for reviewing the fix. > Should you check for the zero case and print a warning? Yes, that would be better. I will post a v2 with that. > > > --- > > drivers/cpuidle/cpuidle-pseries.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c > > index ff6d99e..9043358 100644 > > --- a/drivers/cpuidle/cpuidle-pseries.c > > +++ b/drivers/cpuidle/cpuidle-pseries.c > > @@ -361,7 +361,7 @@ static void __init fixup_cede0_latency(void) > > for (i = 0; i < nr_xcede_records; i++) { > > struct xcede_latency_record *record = &payload->records[i]; > > u64 latency_tb = be64_to_cpu(record->latency_ticks); > > - u64 latency_us = tb_to_ns(latency_tb) / NSEC_PER_USEC; > > + u64 latency_us = DIV_ROUND_UP_ULL(tb_to_ns(latency_tb), NSEC_PER_USEC); > > > > if (latency_us < min_latency_us) > > min_latency_us = latency_us; > > -- > > 1.9.4 > >
diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c index ff6d99e..9043358 100644 --- a/drivers/cpuidle/cpuidle-pseries.c +++ b/drivers/cpuidle/cpuidle-pseries.c @@ -361,7 +361,7 @@ static void __init fixup_cede0_latency(void) for (i = 0; i < nr_xcede_records; i++) { struct xcede_latency_record *record = &payload->records[i]; u64 latency_tb = be64_to_cpu(record->latency_ticks); - u64 latency_us = tb_to_ns(latency_tb) / NSEC_PER_USEC; + u64 latency_us = DIV_ROUND_UP_ULL(tb_to_ns(latency_tb), NSEC_PER_USEC); if (latency_us < min_latency_us) min_latency_us = latency_us;