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From: "Li, Aubrey" <aubrey.li@linux.intel.com>
To: Ingo Molnar <mingo@kernel.org>, Aubrey Li <aubrey.intel@gmail.com>
Cc: "Julien Desfossez" <jdesfossez@digitalocean.com>,
	"Vineeth Remanan Pillai" <vpillai@digitalocean.com>,
	"Nishanth Aravamudan" <naravamudan@digitalocean.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Tim Chen" <tim.c.chen@linux.intel.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Paul Turner" <pjt@google.com>,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	"Linux List Kernel Mailing" <linux-kernel@vger.kernel.org>,
	"Subhra Mazumdar" <subhra.mazumdar@oracle.com>,
	"Frédéric Weisbecker" <fweisbec@gmail.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Greg Kerr" <kerrnel@google.com>, "Phil Auld" <pauld@redhat.com>,
	"Aaron Lu" <aaron.lwe@gmail.com>,
	"Valentin Schneider" <valentin.schneider@arm.com>,
	"Mel Gorman" <mgorman@techsingularity.net>,
	"Pawan Gupta" <pawan.kumar.gupta@linux.intel.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>
Subject: Re: [RFC PATCH v2 00/17] Core scheduling v2
Date: Sat, 18 May 2019 09:08:12 +0800
Message-ID: <44e6eba0-abf1-3251-c16a-96ee28dcc14b@linux.intel.com> (raw)
In-Reply-To: <9489d9e4-1dae-fc84-53eb-beb0c1418c0f@linux.intel.com>

On 2019/5/18 8:58, Li, Aubrey wrote:
> On 2019/4/30 12:42, Ingo Molnar wrote:
>>
>>>> What's interesting is how in the over-saturated case (the last three
>>>> rows: 128, 256 and 512 total threads) coresched-SMT leaves 20-30% CPU
>>>> performance on the floor according to the load figures.
>>>
> 
> Sorry for a delay, I got a chance to obtain some profiling results. Here
> is the story on my side. I still used the previous testing 128/128 case
> (256 threads totally), and focus on CPU53(randomly pickup) only.
> 
> Firstly, mpstat reports cpu utilization,
> - baseline is 100%,
> - coresched-SMT is 87.51%
> 
> Then I traced sched_switch trace point, in 100s sampling period,
> - baseline context switch 14083 times, next task idle 0 times
> - coresched-SMT context switch 15101 times, next task idle 880 times
> 
> So I guess pick_next_task() is mostly the interesting place, then I
> dig into the trace log on coresched-SMT case:
> - CPU53 selected idle task 767 times (matched with the data of sched_switch)
> 
> There are 3 branches of CPU53 selecting idle task in pick_next_task():
> - pick pre selected 765 times
> - unconstrained pick 1 times
> - picked: swapper/53/0 1 times
> 
> Where CPU53's "pick pre selected idle task" from? I guess its from its
> brother CPU1, so I checked CPU1's trace log and found:
> - CPU1 helped its sibling CPU53 select idle task 800 times
> 
> So for CPU53, the most interesting part occurs in pick_task(), that is:
> -The sibling CPU1 helped to select idle task in pick_task()
> 
> Forgive me to paste this routine() here:
> =====================================================
> +// XXX fairness/fwd progress conditions
> +static struct task_struct *
> +pick_task(struct rq *rq, const struct sched_class *class, struct task_struct *max)
> +{
> +	struct task_struct *class_pick, *cookie_pick;
> +	unsigned long cookie = 0UL;
> +
> +	/*
> +	 * We must not rely on rq->core->core_cookie here, because we fail to reset
> +	 * rq->core->core_cookie on new picks, such that we can detect if we need
> +	 * to do single vs multi rq task selection.
> +	 */
> +
> +	if (max && max->core_cookie) {
> +		WARN_ON_ONCE(rq->core->core_cookie != max->core_cookie);
> +		cookie = max->core_cookie;
> +	}
> +
> +	class_pick = class->pick_task(rq);
> +	if (!cookie)
> +		return class_pick;
> +
> +	cookie_pick = sched_core_find(rq, cookie);
> +	if (!class_pick)
> +		return cookie_pick;
> +
> +	/*
> +	 * If class > max && class > cookie, it is the highest priority task on
> +	 * the core (so far) and it must be selected, otherwise we must go with
> +	 * the cookie pick in order to satisfy the constraint.
> +	 */
> +	if (cpu_prio_less(cookie_pick, class_pick) && core_prio_less(max, class_pick))
> +		return class_pick;
> +
> +	return cookie_pick;
> +}
> =================================================================
> 
> And the most related log of the case:
> =================================================================
> <...>-21553 [001] dN.. 87341.514992: __schedule: cpu(1): selected: gemmbench/21294 ffff888823df8900
> <...>-21553 [001] dN.. 87341.514992: __schedule: max: gemmbench/21294 ffff888823df8900
> <...>-21553 [001] dN.. 87341.514995: __schedule: (swapper/53/0;140,0,0) ?< (sysbench/21503;140,457178607302,0)
> <...>-21553 [001] dN.. 87341.514996: __schedule: (gemmbench/21294;119,219715519947,0) ?< (sysbench/21503;119,457178607302,0)
> <...>-21553 [001] dN.. 87341.514996: __schedule: cpu(53): selected: swapper/53/0 0
> 
> It said,
> - CPU1 selected gemmbench for itself
> - and gemmbench was assigned to max of this core
> - then CPU1 helped CPU53 to pick_task()
> -- CPU1 used class->pick_task(), selected sysbench for CPU53
> -- CPU1 used cookie_pick, selected swapper(idle task) for CPU53
> -- the class_pick(sysbench) unfortunately didn't pass the priority check
> - idle task picked up at the end(sadly).
> 
> So, I think if we want to improve CPU utilization under this scenario,
> the straightforward tweak is picking up class_pick if cookie_pick is idle.

Another quick thought is, in CPU53's own path of pick_next_task, give up
pre selected(by CPU1) if pre selected is idle?


> But I know, this is a violation of the design philosophy(avoid L1TF) of
> this proposal.
> 
> Does it make sense to add a knob to switch security/performance?
> Welcome any comments!
> 
> Thanks,
> -Aubrey
> 


  reply index

Thread overview: 109+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-23 16:18 Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 01/17] stop_machine: Fix stop_cpus_in_progress ordering Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 02/17] sched: Fix kerneldoc comment for ia64_set_curr_task Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 03/17] sched: Wrap rq::lock access Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 04/17] sched/{rt,deadline}: Fix set_next_task vs pick_next_task Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 05/17] sched: Add task_struct pointer to sched_class::set_curr_task Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 06/17] sched/fair: Export newidle_balance() Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 07/17] sched: Allow put_prev_task() to drop rq->lock Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 08/17] sched: Rework pick_next_task() slow-path Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 09/17] sched: Introduce sched_class::pick_task() Vineeth Remanan Pillai
2019-04-26 14:02   ` Peter Zijlstra
2019-04-26 16:10     ` Vineeth Remanan Pillai
2019-04-29  5:38   ` Aaron Lu
2019-04-23 16:18 ` [RFC PATCH v2 10/17] sched: Core-wide rq->lock Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 11/17] sched: Basic tracking of matching tasks Vineeth Remanan Pillai
2019-04-24  0:08   ` Tim Chen
2019-04-24 20:43     ` Vineeth Remanan Pillai
2019-04-24 22:12       ` Tim Chen
2019-04-25 14:35       ` Phil Auld
2019-05-22 19:52         ` Vineeth Remanan Pillai
2019-04-24  0:17   ` Tim Chen
2019-04-24 20:43     ` Vineeth Remanan Pillai
2019-04-29  3:36   ` Aaron Lu
2019-05-10 13:06     ` Peter Zijlstra
2019-04-29  6:15   ` Aaron Lu
2019-05-01 23:27     ` Tim Chen
2019-05-03  0:06       ` Tim Chen
2019-05-08 15:49         ` Aubrey Li
2019-05-08 18:19           ` Subhra Mazumdar
2019-05-08 18:37             ` Subhra Mazumdar
2019-05-09  0:01               ` Aubrey Li
2019-05-09  0:25                 ` Subhra Mazumdar
2019-05-09  1:38                   ` Aubrey Li
2019-05-09  2:14                     ` Subhra Mazumdar
2019-05-09 15:10                       ` Aubrey Li
2019-05-09 17:50                         ` Subhra Mazumdar
2019-05-10  0:09                           ` Tim Chen
2019-04-23 16:18 ` [RFC PATCH v2 12/17] sched: A quick and dirty cgroup tagging interface Vineeth Remanan Pillai
2019-04-25 14:26   ` Phil Auld
2019-04-26 14:13     ` Peter Zijlstra
2019-04-26 14:19       ` Phil Auld
2019-05-10 15:12   ` Julien Desfossez
2019-04-23 16:18 ` [RFC PATCH v2 13/17] sched: Add core wide task selection and scheduling Vineeth Remanan Pillai
2019-04-29  7:13   ` Aaron Lu
2019-05-18 15:37   ` Aubrey Li
2019-05-20 13:04     ` Phil Auld
2019-05-20 14:04       ` Vineeth Pillai
2019-05-21  8:19         ` Aubrey Li
2019-05-21 13:24           ` Vineeth Pillai
2019-04-23 16:18 ` [RFC PATCH v2 14/17] sched/fair: Add a few assertions Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 15/17] sched: Trivial forced-newidle balancer Vineeth Remanan Pillai
2019-04-23 23:46   ` Aubrey Li
2019-04-24 14:03     ` Vineeth Remanan Pillai
2019-04-24 14:05     ` Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 16/17] sched: Wake up sibling if it has something to run Vineeth Remanan Pillai
2019-04-26 15:03   ` Peter Zijlstra
2019-04-29 12:36     ` Julien Desfossez
2019-04-23 16:18 ` [RFC PATCH v2 17/17] sched: Debug bits Vineeth Remanan Pillai
2019-05-17 17:18   ` Aubrey Li
2019-04-23 18:02 ` [RFC PATCH v2 00/17] Core scheduling v2 Phil Auld
2019-04-23 18:45   ` Vineeth Remanan Pillai
2019-04-29  3:53     ` Aaron Lu
2019-05-06 19:39       ` Julien Desfossez
2019-05-08  2:30         ` Aaron Lu
2019-05-08 17:49           ` Julien Desfossez
2019-05-09  2:11             ` Aaron Lu
2019-05-15 21:36               ` Vineeth Remanan Pillai
2019-04-23 23:25 ` Aubrey Li
2019-04-24 11:19   ` Vineeth Remanan Pillai
2019-05-15 21:39     ` Vineeth Remanan Pillai
2019-04-24 13:13 ` Aubrey Li
2019-04-24 14:00   ` Julien Desfossez
2019-04-25  3:15     ` Aubrey Li
2019-04-25  9:55       ` Ingo Molnar
2019-04-25 14:46         ` Mel Gorman
2019-04-25 18:53           ` Ingo Molnar
2019-04-25 18:59             ` Thomas Gleixner
2019-04-25 19:34               ` Ingo Molnar
2019-04-25 21:31             ` Mel Gorman
2019-04-26  8:42               ` Ingo Molnar
2019-04-26 10:43                 ` Mel Gorman
2019-04-26 18:37                   ` Subhra Mazumdar
2019-04-26 19:49                     ` Mel Gorman
2019-04-26  9:45               ` Ingo Molnar
2019-04-26 10:19                 ` Mel Gorman
2019-04-27  9:06                   ` Ingo Molnar
2019-04-26  9:51               ` Ingo Molnar
2019-04-26 14:15             ` Phil Auld
2019-04-26  2:18         ` Aubrey Li
2019-04-26  9:51           ` Ingo Molnar
2019-04-27  3:51         ` Aubrey Li
2019-04-27  9:17           ` Ingo Molnar
2019-04-27 14:04             ` Aubrey Li
2019-04-27 14:21               ` Ingo Molnar
2019-04-27 15:54                 ` Aubrey Li
2019-04-28  9:33                   ` Ingo Molnar
2019-04-28 10:29                     ` Aubrey Li
2019-04-28 12:17                       ` Ingo Molnar
2019-04-29  2:17                         ` Li, Aubrey
2019-04-29  6:14                           ` Ingo Molnar
2019-04-29 13:25                             ` Li, Aubrey
2019-04-29 15:39                               ` Phil Auld
2019-04-30  1:24                                 ` Aubrey Li
2019-04-29 16:00                               ` Ingo Molnar
2019-04-30  1:34                                 ` Aubrey Li
2019-04-30  4:42                                   ` Ingo Molnar
2019-05-18  0:58                                     ` Li, Aubrey
2019-05-18  1:08                                       ` Li, Aubrey [this message]
2019-04-25 14:36 ` Julien Desfossez

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