From: Vincent Guittot <vincent.guittot@linaro.org>
To: Qais Yousef <qais.yousef@arm.com>
Cc: Mel Gorman <mgorman@suse.de>,
Patrick Bellasi <patrick.bellasi@matbug.net>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Randy Dunlap <rdunlap@infradead.org>,
Jonathan Corbet <corbet@lwn.net>,
Juri Lelli <juri.lelli@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>,
Luis Chamberlain <mcgrof@kernel.org>,
Kees Cook <keescook@chromium.org>,
Iurii Zaikin <yzaikin@google.com>,
Quentin Perret <qperret@google.com>,
Valentin Schneider <valentin.schneider@arm.com>,
Pavan Kondeti <pkondeti@codeaurora.org>,
linux-doc@vger.kernel.org,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-fs <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default boost value
Date: Thu, 4 Jun 2020 14:14:40 +0200 [thread overview]
Message-ID: <CAKfTPtC6TvUL83VdWuGfbKm0CkXB85YQ5qkagK9aiDB8Hqrn_Q@mail.gmail.com> (raw)
In-Reply-To: <20200603165200.v2ypeagziht7kxdw@e107158-lin.cambridge.arm.com>
On Wed, 3 Jun 2020 at 18:52, Qais Yousef <qais.yousef@arm.com> wrote:
>
> On 06/03/20 16:59, Vincent Guittot wrote:
> > When I want to stress the fast path i usually use "perf bench sched pipe -T "
> > The tip/sched/core on my arm octo core gives the following results for
> > 20 iterations of perf bench sched pipe -T -l 50000
> >
> > all uclamp config disabled 50035.4(+/- 0.334%)
> > all uclamp config enabled 48749.8(+/- 0.339%) -2.64%
> >
> > It's quite easy to reproduce and probably easier to study the impact
>
> Thanks Vincent. This is very useful!
>
> I could reproduce that on my Juno.
>
> One of the codepath I was suspecting seems to affect it.
>
>
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0464569f26a7..9f48090eb926 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1063,10 +1063,12 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
> * e.g. due to future modification, warn and fixup the expected value.
> */
> SCHED_WARN_ON(bucket->value > rq_clamp);
> +#if 0
> if (bucket->value >= rq_clamp) {
> bkt_clamp = uclamp_rq_max_value(rq, clamp_id, uc_se->value);
> WRITE_ONCE(uc_rq->value, bkt_clamp);
> }
> +#endif
> }
>
> static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
>
>
>
> uclamp_rq_max_value() could be expensive as it loops over all buckets.
> Commenting this whole path out strangely doesn't just 'fix' it, but produces
> better results to no-uclamp kernel :-/
>
>
>
> # ./perf bench -r 20 sched pipe -T -l 50000
> Without uclamp: 5039
> With uclamp: 4832
> With uclamp+patch: 5729
>
>
>
> It might be because schedutil gets biased differently by uclamp..? If I move to
> performance governor these numbers almost double.
>
> I don't know. But this promoted me to look closer and I think I spotted a bug
> where in the if condition we check for '>=' instead of '>', causing us to take
> the supposedly impossible fail safe path.
>
> Mind trying with the below patch please?
I have tried your patch and I don't see any difference compared to
previous tests. Let me give you more details of my setup:
I create 3 levels of cgroups and usually run the tests in the 4 levels
(which includes root). The result above are for the root level
But I see a difference at other levels:
root level 1 level 2 level 3
/w patch uclamp disable 50097 46615 43806 41078
tip uclamp enable 48706(-2.78%) 45583(-2.21%) 42851(-2.18%)
40313(-1.86%)
/w patch uclamp enable 48882(-2.43%) 45774(-1.80%) 43108(-1.59%)
40667(-1.00%)
Whereas tip with uclamp stays around 2% behind tip without uclamp, the
diff of uclamp with your patch tends to decrease when we increase the
number of level
Beside this, that's also interesting to notice the ~6% of perf impact
between each level for the same image
>
>
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0464569f26a7..50d66d4016ff 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1063,7 +1063,7 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
> * e.g. due to future modification, warn and fixup the expected value.
> */
> SCHED_WARN_ON(bucket->value > rq_clamp);
> - if (bucket->value >= rq_clamp) {
> + if (bucket->value > rq_clamp) {
> bkt_clamp = uclamp_rq_max_value(rq, clamp_id, uc_se->value);
> WRITE_ONCE(uc_rq->value, bkt_clamp);
> }
>
>
>
> Thanks
>
> --
> Qais Yousef
next prev parent reply other threads:[~2020-06-04 12:14 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-11 15:40 [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default boost value Qais Yousef
2020-05-11 15:40 ` [PATCH 2/2] Documentation/sysctl: Document uclamp sysctl knobs Qais Yousef
2020-05-11 17:18 ` [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default boost value Qais Yousef
2020-05-12 2:10 ` Pavan Kondeti
2020-05-12 11:46 ` Qais Yousef
2020-05-15 11:08 ` Patrick Bellasi
2020-05-18 8:31 ` Dietmar Eggemann
2020-05-18 16:49 ` Qais Yousef
2020-05-28 13:23 ` Peter Zijlstra
2020-05-28 15:58 ` Qais Yousef
2020-05-28 16:11 ` Peter Zijlstra
2020-05-28 16:51 ` Qais Yousef
2020-05-28 18:29 ` Peter Zijlstra
2020-05-28 19:08 ` Patrick Bellasi
2020-05-28 19:20 ` Dietmar Eggemann
2020-05-29 9:11 ` Qais Yousef
2020-05-29 10:21 ` Mel Gorman
2020-05-29 15:11 ` Qais Yousef
2020-05-29 16:02 ` Mel Gorman
2020-05-29 16:05 ` Qais Yousef
2020-05-29 10:08 ` Mel Gorman
2020-05-29 16:04 ` Qais Yousef
2020-05-29 16:57 ` Mel Gorman
2020-06-02 16:46 ` Dietmar Eggemann
2020-06-03 8:29 ` Patrick Bellasi
2020-06-03 10:10 ` Mel Gorman
2020-06-03 14:59 ` Vincent Guittot
2020-06-03 16:52 ` Qais Yousef
2020-06-04 12:14 ` Vincent Guittot [this message]
2020-06-05 10:45 ` Qais Yousef
2020-06-09 15:29 ` Vincent Guittot
2020-06-08 12:31 ` Qais Yousef
2020-06-08 13:06 ` Valentin Schneider
2020-06-08 14:44 ` Steven Rostedt
2020-06-11 10:13 ` Qais Yousef
2020-06-09 17:10 ` Vincent Guittot
2020-06-11 10:24 ` Qais Yousef
2020-06-11 12:01 ` Vincent Guittot
2020-06-23 15:44 ` Qais Yousef
2020-06-24 8:45 ` Vincent Guittot
2020-06-05 7:55 ` Patrick Bellasi
2020-06-05 11:32 ` Qais Yousef
2020-06-05 13:27 ` Patrick Bellasi
2020-06-03 9:40 ` Mel Gorman
2020-06-03 12:41 ` Qais Yousef
2020-06-04 13:40 ` Mel Gorman
2020-06-05 10:58 ` Qais Yousef
2020-06-11 10:58 ` Qais Yousef
2020-06-16 11:08 ` Qais Yousef
2020-06-16 13:56 ` Lukasz Luba
-- strict thread matches above, loose matches on Subject: below --
2020-04-03 12:30 Qais Yousef
2020-04-14 18:21 ` Patrick Bellasi
2020-04-15 7:46 ` Patrick Bellasi
2020-04-20 15:04 ` Qais Yousef
2020-04-20 8:24 ` Dietmar Eggemann
2020-04-20 15:19 ` Qais Yousef
2020-04-21 0:52 ` Steven Rostedt
2020-04-21 11:16 ` Dietmar Eggemann
2020-04-21 11:23 ` Qais Yousef
2020-04-20 14:50 ` Qais Yousef
2020-04-15 10:11 ` Quentin Perret
2020-04-20 15:08 ` Qais Yousef
2020-04-20 8:29 ` Dietmar Eggemann
2020-04-20 15:13 ` Qais Yousef
2020-04-21 11:18 ` Dietmar Eggemann
2020-04-21 11:27 ` Qais Yousef
2020-04-22 10:59 ` Dietmar Eggemann
2020-04-22 13:13 ` Qais Yousef
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=CAKfTPtC6TvUL83VdWuGfbKm0CkXB85YQ5qkagK9aiDB8Hqrn_Q@mail.gmail.com \
--to=vincent.guittot@linaro.org \
--cc=bsegall@google.com \
--cc=corbet@lwn.net \
--cc=dietmar.eggemann@arm.com \
--cc=juri.lelli@redhat.com \
--cc=keescook@chromium.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mcgrof@kernel.org \
--cc=mgorman@suse.de \
--cc=mingo@redhat.com \
--cc=patrick.bellasi@matbug.net \
--cc=peterz@infradead.org \
--cc=pkondeti@codeaurora.org \
--cc=qais.yousef@arm.com \
--cc=qperret@google.com \
--cc=rdunlap@infradead.org \
--cc=rostedt@goodmis.org \
--cc=valentin.schneider@arm.com \
--cc=yzaikin@google.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).