LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Viresh Kumar <viresh.kumar@linaro.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Rafael Wysocki <rjw@rjwysocki.net>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Claudio Scordino <claudio@evidence.eu.com>,
	Patrick Bellasi <patrick.bellasi@arm.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Joel Fernandes <joelaf@google.com>,
	"4 . 12+" <stable@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] sched/schedutil: Don't set next_freq to UINT_MAX
Date: Wed, 9 May 2018 15:00:23 +0530	[thread overview]
Message-ID: <20180509093023.7ex7lglfxo22stgn@vireshk-i7> (raw)
In-Reply-To: <CAJZ5v0jekW=8-VbeVR5GZ6iTxj_oHiFAq7OWqzkAWktL2pU=CA@mail.gmail.com>

On 09-05-18, 11:23, Rafael J. Wysocki wrote:
> On Wed, May 9, 2018 at 11:15 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> > On 09-05-18, 10:56, Rafael J. Wysocki wrote:
> >> I'm kind of concerned about updating the limits via sysfs in which
> >> case the cached next frequency may be out of range, so it's better to
> >> invalidate it right away then.
> >
> > That should not be a problem as __cpufreq_driver_target() will anyway
> > clamp the target frequency to be within limits, whatever the cached
> > value of next_freq is.
> 
> The fast switch case doesn't use it, though.

cpufreq_driver_fast_switch() does the same clamping :)

> > And we aren't invalidating the cached next freq immediately currently
> > as well, as we are waiting until the next time the util update handler
> > is called to set sg_policy->next_freq to UINT_MAX.
> >
> >> > What else do you have in mind to solve this problem ?
> >>
> >> Something like the below?
> >>
> >> ---
> >>  kernel/sched/cpufreq_schedutil.c |    3 ++-
> >>  1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> Index: linux-pm/kernel/sched/cpufreq_schedutil.c
> >> ===================================================================
> >> --- linux-pm.orig/kernel/sched/cpufreq_schedutil.c
> >> +++ linux-pm/kernel/sched/cpufreq_schedutil.c
> >> @@ -305,7 +305,8 @@ static void sugov_update_single(struct u
> >>       * Do not reduce the frequency if the CPU has not been idle
> >>       * recently, as the reduction is likely to be premature then.
> >>       */
> >> -    if (busy && next_f < sg_policy->next_freq) {
> >> +    if (busy && next_f < sg_policy->next_freq &&
> >> +        sg_policy->next_freq != UINT_MAX) {
> >>          next_f = sg_policy->next_freq;
> >>
> >>          /* Reset cached freq as next_freq has changed */
> >
> > This will fix the problem we have identified currently, but adding a
> > special meaning to next_freq == UINT_MAX invites more hidden corner
> > cases like the one we just found. IMHO, using next_freq only for the
> > *real* frequency values makes its usage more transparent and readable.
> > And we already have the need_freq_update flag which we can use for
> > this special purpose, as is done in my patch.
> 
> So I prefer to do the above as a -stable fix and make the UNIT_MAX
> change on top of that.

Okay, that's fine with me. Will send the next version now :)

Just to make sure, you are fine with the "Fixes" tag now (since you
objected to that earlier) ?

-- 
viresh

  reply	other threads:[~2018-05-09  9:30 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-08  6:42 Viresh Kumar
2018-05-08 20:54 ` Rafael J. Wysocki
2018-05-09  8:41   ` Viresh Kumar
2018-05-09  8:56     ` Rafael J. Wysocki
2018-05-09  9:15       ` Viresh Kumar
2018-05-09  9:23         ` Rafael J. Wysocki
2018-05-09  9:30           ` Viresh Kumar [this message]
2018-05-09  9:32             ` Rafael J. Wysocki
2018-05-09  9:44 ` [PATCH] cpufreq: schedutil: Avoid using invalid next_freq Rafael J. Wysocki
2018-05-09  9:46   ` Viresh Kumar
2018-05-09 10:35   ` [PATCH V2] sched/schedutil: Don't set next_freq to UINT_MAX Viresh Kumar
2018-05-11 20:47     ` [V2] " Joel Fernandes
2018-05-17 10:33       ` Rafael J. Wysocki

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180509093023.7ex7lglfxo22stgn@vireshk-i7 \
    --to=viresh.kumar@linaro.org \
    --cc=claudio@evidence.eu.com \
    --cc=joelaf@google.com \
    --cc=juri.lelli@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pm@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=patrick.bellasi@arm.com \
    --cc=peterz@infradead.org \
    --cc=rafael@kernel.org \
    --cc=rjw@rjwysocki.net \
    --cc=stable@vger.kernel.org \
    --cc=vincent.guittot@linaro.org \
    --subject='Re: [PATCH] sched/schedutil: Don'\''t set next_freq to UINT_MAX' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).