From: Qais Yousef <qyousef@layalina.io>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Wyes Karny <wkarny@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Juri Lelli <juri.lelli@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Valentin Schneider <vschneid@redhat.com>
Subject: Re: [GIT PULL] Scheduler changes for v6.8
Date: Sun, 14 Jan 2024 23:37:28 +0000 [thread overview]
Message-ID: <20240114233728.hrmyelo66beaajhp@airbuntu> (raw)
In-Reply-To: <20240114195815.nes4bn53tc25djbh@airbuntu>
[-- Attachment #1: Type: text/plain, Size: 3634 bytes --]
On 01/14/24 19:58, Qais Yousef wrote:
> > This is not correct because you will have to wait to reach full
> > utilization at the current OPP possibly the lowest OPP before moving
> > directly to max OPP
>
> Isn't this already the case? The ratio (util+headroom/max) will be less than
> 1 until util is 80% (with 25% headroom). And for all values <= 80% * max, we
> will request a frequency smaller than/equal policy->cur, no?
>
> ie:
>
> util = 600
> max = 1024
>
> freq = 1.25 * 600 * policy->cur / 1024 = 0.73 * policy->cur
>
> (util+headroom/max) must be greater than 1 for us to start going above
> policy->cur - which seems to have been working by accident IIUC.
>
> So yes my proposal is incorrect, but it seems the conversion is not right to me
> now.
>
> I could reproduce the problem now (thanks Wyes!). I have 3 freqs on my system
>
> 2.2GHz, 2.8GHz and 3.8GHz
>
> which (I believe) translates into capacities
>
> ~592, ~754, 1024
>
> which means we should pick 2.8GHz as soon as util * 1.25 > 592; which
> translates into util = ~473.
>
> But what I see is that we go to 2.8GHz when we jump from 650 to 680 (see
> attached picture), which is what you'd expect since we apply two headrooms now,
> which means the ratio (util+headroom/max) will be greater than 1 after go above
> this value
>
> 1024 * 0.8 * 0.8 = ~655
>
> So I think the math makes sense logically, but we're missing some other
> correction factor.
>
> When I re-enable CPPC I see for the same test that we go into 3.8GHz straight
> away. My test is simple busyloop via
>
> cat /dev/zero > /dev/null
>
> I see the CPU util_avg is at 523 at fork. I expected us to run to 2.8GHz here
> to be honest, but I am not sure if util_cfs_boost() and util_est() are maybe
> causing us to be slightly above 523 and that's why we start with max freq.
>
> Or I've done the math wrong :-) But the two don't behave the same for the same
> kernel with and without CPPC.
I think the relationship should be:
freq = util * f_curr / cap_curr
(patch below)
with that I see (almost) the expected behavior (picture attached). We go to
2.8GHz when we are above 500. But the move to 3.8GHz is a bit earlier at 581
(instead of 754 * 0.8 = 603). Not sure why. With 25% headroom 581 is 726. So
it's a tad too early.
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 95c3c097083e..155f96a44fa0 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -123,7 +123,8 @@ static void sugov_deferred_update(struct sugov_policy *sg_policy)
* Return: the reference CPU frequency to compute a capacity.
*/
static __always_inline
-unsigned long get_capacity_ref_freq(struct cpufreq_policy *policy)
+unsigned long get_capacity_ref_freq(struct cpufreq_policy *policy,
+ unsigned long *max)
{
unsigned int freq = arch_scale_freq_ref(policy->cpu);
@@ -133,6 +134,9 @@ unsigned long get_capacity_ref_freq(struct cpufreq_policy *policy)
if (arch_scale_freq_invariant())
return policy->cpuinfo.max_freq;
+ if (max)
+ *max = policy->cur * (*max) / policy->cpuinfo.max_freq;
+
return policy->cur;
}
@@ -164,7 +168,7 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
struct cpufreq_policy *policy = sg_policy->policy;
unsigned int freq;
- freq = get_capacity_ref_freq(policy);
+ freq = get_capacity_ref_freq(policy, &max);
freq = map_util_freq(util, freq, max);
if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
[-- Attachment #2: cppc_freq_fix2.png --]
[-- Type: image/png, Size: 30853 bytes --]
next prev parent reply other threads:[~2024-01-14 23:37 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-28 12:23 [GIT PULL] Scheduler changes for v6.7 Ingo Molnar
2023-10-30 23:50 ` pr-tracker-bot
2024-01-08 14:07 ` [GIT PULL] Scheduler changes for v6.8 Ingo Molnar
2024-01-09 4:04 ` pr-tracker-bot
2024-01-10 22:19 ` Linus Torvalds
2024-01-10 22:41 ` Linus Torvalds
2024-01-10 22:57 ` Linus Torvalds
2024-01-11 8:11 ` Vincent Guittot
2024-01-11 17:45 ` Linus Torvalds
2024-01-11 17:53 ` Linus Torvalds
2024-01-11 18:16 ` Vincent Guittot
2024-01-12 14:23 ` Dietmar Eggemann
2024-01-12 16:58 ` Vincent Guittot
2024-01-12 18:18 ` Qais Yousef
2024-01-12 19:03 ` Vincent Guittot
2024-01-12 20:30 ` Linus Torvalds
2024-01-12 20:49 ` Linus Torvalds
2024-01-12 21:04 ` Linus Torvalds
2024-01-13 1:04 ` Qais Yousef
2024-01-13 1:24 ` Linus Torvalds
2024-01-13 1:31 ` Linus Torvalds
2024-01-13 10:47 ` Vincent Guittot
2024-01-13 18:33 ` Qais Yousef
2024-01-13 18:37 ` Qais Yousef
2024-01-11 11:09 ` [GIT PULL] scheduler fixes Ingo Molnar
2024-01-11 13:04 ` Vincent Guittot
2024-01-11 20:48 ` [PATCH] Revert "sched/cpufreq: Rework schedutil governor performance estimation" and dependent commit Ingo Molnar
2024-01-11 22:22 ` Vincent Guittot
2024-01-12 18:24 ` Ingo Molnar
2024-01-12 18:26 ` [GIT PULL] Scheduler changes for v6.8 Ingo Molnar
2024-01-14 9:12 ` Wyes Karny
2024-01-14 11:18 ` Vincent Guittot
2024-01-14 12:37 ` Wyes Karny
2024-01-14 13:02 ` Dietmar Eggemann
2024-01-14 13:05 ` Vincent Guittot
2024-01-14 13:03 ` Vincent Guittot
2024-01-14 15:12 ` Qais Yousef
2024-01-14 15:20 ` Vincent Guittot
2024-01-14 19:58 ` Qais Yousef
2024-01-14 23:37 ` Qais Yousef [this message]
2024-01-15 6:25 ` Wyes Karny
2024-01-15 11:59 ` Qais Yousef
2024-01-15 8:21 ` Vincent Guittot
2024-01-15 12:09 ` Qais Yousef
2024-01-15 13:26 ` Vincent Guittot
2024-01-15 14:03 ` Dietmar Eggemann
2024-01-15 15:26 ` Vincent Guittot
2024-01-15 20:05 ` Dietmar Eggemann
2024-01-15 8:42 ` David Laight
2024-01-14 18:11 ` Wyes Karny
2024-01-14 18:18 ` Vincent Guittot
2024-01-11 9:33 ` Ingo Molnar
2024-01-11 11:14 ` [tip: sched/urgent] Revert "sched/cpufreq: Rework schedutil governor performance estimation" and dependent commits tip-bot2 for Ingo Molnar
2024-01-11 20:55 ` [tip: sched/urgent] Revert "sched/cpufreq: Rework schedutil governor performance estimation" and dependent commit tip-bot2 for Ingo Molnar
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=20240114233728.hrmyelo66beaajhp@airbuntu \
--to=qyousef@layalina.io \
--cc=bristot@redhat.com \
--cc=bsegall@google.com \
--cc=dietmar.eggemann@arm.com \
--cc=juri.lelli@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
--cc=vincent.guittot@linaro.org \
--cc=vschneid@redhat.com \
--cc=wkarny@gmail.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).