Messages in this thread | | | From | Joel Stanley <> | Date | Wed, 2 Sep 2020 01:08:35 +0000 | Subject | Re: [PATCH] cpuidle-pseries: Fix CEDE latency conversion from tb to us |
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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>
Should you check for the zero case and print a warning?
> --- > 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 >
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