From: Joel Stanley <joel@jms.id.au> To: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> Cc: Michael Ellerman <mpe@ellerman.id.au>, "Rafael J. Wysocki" <rjw@rjwysocki.net>, Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>, linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-pm@vger.kernel.org Subject: Re: [PATCH] cpuidle-pseries: Fix CEDE latency conversion from tb to us Date: Wed, 2 Sep 2020 01:08:35 +0000 [thread overview] Message-ID: <CACPK8XfZdnKusEuu8i=-aH=Wfr6X6sMrvX=btFq9PtnXJ2w-SQ@mail.gmail.com> (raw) In-Reply-To: <1598969293-29228-1-git-send-email-ego@linux.vnet.ibm.com> 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 >
WARNING: multiple messages have this Message-ID (diff)
From: Joel Stanley <joel@jms.id.au> To: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> Cc: linux-pm@vger.kernel.org, "Rafael J. Wysocki" <rjw@rjwysocki.net>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>, linuxppc-dev <linuxppc-dev@lists.ozlabs.org> Subject: Re: [PATCH] cpuidle-pseries: Fix CEDE latency conversion from tb to us Date: Wed, 2 Sep 2020 01:08:35 +0000 [thread overview] Message-ID: <CACPK8XfZdnKusEuu8i=-aH=Wfr6X6sMrvX=btFq9PtnXJ2w-SQ@mail.gmail.com> (raw) In-Reply-To: <1598969293-29228-1-git-send-email-ego@linux.vnet.ibm.com> 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 >
next prev parent reply other threads:[~2020-09-02 1:08 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-09-01 14:08 [PATCH] cpuidle-pseries: Fix CEDE latency conversion from tb to us Gautham R. Shenoy 2020-09-01 14:08 ` Gautham R. Shenoy 2020-09-02 1:08 ` Joel Stanley [this message] 2020-09-02 1:08 ` Joel Stanley 2020-09-02 8:35 ` Gautham R Shenoy 2020-09-02 8:35 ` Gautham R Shenoy
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