From: Valentin Schneider <valentin.schneider@arm.com>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Mel Gorman <mgorman@techsingularity.net>,
Rik van Riel <riel@surriel.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Gautham R Shenoy <ego@linux.vnet.ibm.com>,
Parth Shah <parth@linux.ibm.com>
Subject: Re: [PATCH v2 2/8] sched/fair: Maintain the identity of idle-core
Date: Tue, 11 May 2021 12:51:26 +0100 [thread overview]
Message-ID: <87v97p1oap.mognet@arm.com> (raw)
In-Reply-To: <20210506164543.90688-3-srikar@linux.vnet.ibm.com>
On 06/05/21 22:15, Srikar Dronamraju wrote:
> Scheduler maintains a per LLC info which tells if there is any idle core
> in that LLC. However this information doesn't provide which core is idle.
>
> So when iterating for idle-cores, if select_idle_core() finds an
> idle-core, then it doesn't try to reset this information.
>
> So if there was only one idle core in the LLC and select_idle_core()
> selected the idle-core, the LLC will maintain that it still has a
> idle-core.
>
That would be rectified at the next select_idle_cpu() call, so that would
be a fight between extra instrumentation overhead vs extra work at next
wakeup.
> On the converse, if a task is pinned, and has a restricted
> cpus_allowed_list and LLC has multiple idle-cores, but select_idle_core
> cannot find a idle-core, LLC will no more maintain that it has an
> idle-core.
>
This however does sound icky.
> As a first step to solve this problem, LLC will maintain the identity of
> the idle core instead of just the information that LLC has an idle core
>
> Along with maintaining, this change will solve both the problems listed
> above. However there are other problems that exist with the current
> infrastructure and those will continue to exist with this change and
> would be handled in subsequent patches.
>
> Cc: LKML <linux-kernel@vger.kernel.org>
> Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
> Cc: Parth Shah <parth@linux.ibm.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Valentin Schneider <valentin.schneider@arm.com>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Rik van Riel <riel@surriel.com>
> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> ---
> @@ -6127,7 +6129,8 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
> {
> struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
> int i, cpu, idle_cpu = -1, nr = INT_MAX;
> - bool smt = test_idle_cores(target, false);
> + int idle_core = get_idle_core(target, -1);
> + bool smt = (idle_core != -1);
test_idle_cores() tells you if there's at least one idle core in the
target's LLC. AFAICT get_idle_core() only tells you whether the target's
core is idle, which is not the same thing.
Note that this code has recently been changed by Rik in
c722f35b513f ("sched/fair: Bring back select_idle_smt(), but differently")
so as annoying as it is you should probably go try this out / rebase your
series on top of it (as a rule of thumb for core scheduler stuff you should
use https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git -b
tip/sched/core as a base).
next prev parent reply other threads:[~2021-05-11 11:51 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-06 16:45 [PATCH v2 0/8] sched/fair: wake_affine improvements Srikar Dronamraju
2021-05-06 16:45 ` [PATCH v2 1/8] sched/fair: Update affine statistics when needed Srikar Dronamraju
2021-05-07 16:08 ` Valentin Schneider
2021-05-07 17:05 ` Srikar Dronamraju
2021-05-11 11:51 ` Valentin Schneider
2021-05-11 16:22 ` Srikar Dronamraju
2021-05-06 16:45 ` [PATCH v2 2/8] sched/fair: Maintain the identity of idle-core Srikar Dronamraju
2021-05-11 11:51 ` Valentin Schneider [this message]
2021-05-11 16:27 ` Srikar Dronamraju
2021-05-06 16:45 ` [PATCH v2 3/8] sched/fair: Update idle-core more often Srikar Dronamraju
2021-05-06 16:45 ` [PATCH v2 4/8] sched/fair: Prefer idle CPU to cache affinity Srikar Dronamraju
2021-05-06 16:45 ` [PATCH v2 5/8] sched/fair: Use affine_idler_llc for wakeups across LLC Srikar Dronamraju
2021-05-06 16:45 ` [PATCH v2 6/8] sched/idle: Move busy_cpu accounting to idle callback Srikar Dronamraju
2021-05-11 11:51 ` Valentin Schneider
2021-05-11 16:55 ` Srikar Dronamraju
2021-05-12 0:32 ` Aubrey Li
2021-05-12 8:08 ` Aubrey Li
2021-05-13 7:31 ` Srikar Dronamraju
2021-05-14 4:11 ` Aubrey Li
2021-05-17 10:40 ` Srikar Dronamraju
2021-05-17 12:48 ` Aubrey Li
2021-05-17 12:57 ` Srikar Dronamraju
2021-05-18 0:59 ` Aubrey Li
2021-05-18 4:00 ` Srikar Dronamraju
2021-05-18 6:05 ` Aubrey Li
2021-05-18 7:18 ` Srikar Dronamraju
2021-05-19 9:43 ` Aubrey Li
2021-05-19 17:34 ` Srikar Dronamraju
2021-05-06 16:45 ` [PATCH v2 7/8] sched/fair: Remove ifdefs in waker_affine_idler_llc Srikar Dronamraju
2021-05-06 16:45 ` [PATCH v2 8/8] sched/fair: Dont iterate if no idle CPUs Srikar Dronamraju
2021-05-06 16:53 ` [PATCH v2 0/8] sched/fair: wake_affine improvements Srikar Dronamraju
-- strict thread matches above, loose matches on Subject: below --
2021-05-06 20:24 [PATCH v2 2/8] sched/fair: Maintain the identity of idle-core kernel test robot
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