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From: "Li, Aubrey" <aubrey.li@linux.intel.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: "Ning, Hongyu" <hongyu.ning@linux.intel.com>,
	Nishanth Aravamudan <naravamudan@digitalocean.com>,
	Julien Desfossez <jdesfossez@digitalocean.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Vineeth Pillai <viremana@linux.microsoft.com>,
	Aaron Lu <aaron.lwe@gmail.com>,
	Aubrey Li <aubrey.intel@gmail.com>,
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	mingo@kernel.org, torvalds@linux-foundation.org,
	fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com,
	Phil Auld <pauld@redhat.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>,
	vineeth@bitbyteword.org, Chen Yu <yu.c.chen@intel.com>,
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	Agata Gruza <agata.gruza@intel.com>,
	Antonio Gomez Iglesias <antonio.gomez.iglesias@intel.com>,
	graf@amazon.com, konrad.wilk@oracle.com, dfaggioli@suse.com,
	pjt@google.com, rostedt@goodmis.org, derkling@google.com,
	benbjiang@tencent.com,
	Alexandre Chartre <alexandre.chartre@oracle.com>,
	James.Bottomley@hansenpartnership.com, OWeisse@umich.edu,
	Dhaval Giani <dhaval.giani@oracle.com>,
	Junaid Shahid <junaids@google.com>,
	jsbarnes@google.com, chris.hyser@oracle.com,
	Tim Chen <tim.c.chen@intel.com>
Subject: Re: [PATCH v8 -tip 00/26] Core scheduling
Date: Mon, 9 Nov 2020 14:04:13 +0800	[thread overview]
Message-ID: <389de3ef-2e1f-c569-d3c8-eebb4e6b6bd1@linux.intel.com> (raw)
In-Reply-To: <20201106175427.GB2845264@google.com>

On 2020/11/7 1:54, Joel Fernandes wrote:
> On Fri, Nov 06, 2020 at 10:58:58AM +0800, Li, Aubrey wrote:
> 
>>>
>>> 	-- workload D, new added syscall workload, performance drop in cs_on:
>>> 	+----------------------+------+-------------------------------+
>>> 	|                      | **   | will-it-scale  * 192          |
>>> 	|                      |      | (pipe based context_switch)   |
>>> 	+======================+======+===============================+
>>> 	| cgroup               | **   | cg_will-it-scale              |
>>> 	+----------------------+------+-------------------------------+
>>> 	| record_item          | **   | threads_avg                   |
>>> 	+----------------------+------+-------------------------------+
>>> 	| coresched_normalized | **   | 0.2                           |
>>> 	+----------------------+------+-------------------------------+
>>> 	| default_normalized   | **   | 1                             |
>>> 	+----------------------+------+-------------------------------+
>>> 	| smtoff_normalized    | **   | 0.89                          |
>>> 	+----------------------+------+-------------------------------+
>>
>> will-it-scale may be a very extreme case. The story here is,
>> - On one sibling reader/writer gets blocked and tries to schedule another reader/writer in.
>> - The other sibling tries to wake up reader/writer.
>>
>> Both CPUs are acquiring rq->__lock,
>>
>> So when coresched off, they are two different locks, lock stat(1 second delta) below:
>>
>> class name    con-bounces    contentions   waittime-min   waittime-max waittime-total   waittime-avg    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total   holdtime-avg
>> &rq->__lock:          210            210           0.10           3.04         180.87           0.86            797       79165021           0.03          20.69    60650198.34           0.77
>>
>> But when coresched on, they are actually one same lock, lock stat(1 second delta) below:
>>
>> class name    con-bounces    contentions   waittime-min   waittime-max waittime-total   waittime-avg    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total   holdtime-avg
>> &rq->__lock:      6479459        6484857           0.05         216.46    60829776.85           9.38        8346319       15399739           0.03          95.56    81119515.38           5.27
>>
>> This nature of core scheduling may degrade the performance of similar workloads with frequent context switching.
> 
> When core sched is off, is SMT off as well? From the above table, it seems to
> be. So even for core sched off, there will be a single lock per physical CPU
> core (assuming SMT is also off) right? Or did I miss something?
> 

The table includes 3 cases:
- default:	SMT on,  coresched off
- coresched:	SMT on,  coresched on
- smtoff:	SMT off, coresched off

I was comparing the default(coresched off & SMT on) case with (coresched
on & SMT on) case.

If SMT off, then reader and writer on the different cores have different rq->lock,
so the lock contention is not that serious.

class name    con-bounces    contentions   waittime-min   waittime-max waittime-total   waittime-avg    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total   holdtime-avg
&rq->__lock:           60             60           0.11           1.92          41.33           0.69            127       67184172           0.03          22.95    33160428.37           0.49

Does this address your concern?

Thanks,
-Aubrey


  reply	other threads:[~2020-11-09  6:04 UTC|newest]

Thread overview: 98+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-20  1:43 [PATCH v8 -tip 00/26] Core scheduling Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 01/26] sched: Wrap rq::lock access Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 02/26] sched: Introduce sched_class::pick_task() Joel Fernandes (Google)
2020-10-22  7:59   ` Li, Aubrey
2020-10-22 15:25     ` Joel Fernandes
2020-10-23  5:25       ` Li, Aubrey
2020-10-23 21:47         ` Joel Fernandes
2020-10-24  2:48           ` Li, Aubrey
2020-10-24 11:10             ` Vineeth Pillai
2020-10-24 12:27               ` Vineeth Pillai
2020-10-24 23:48                 ` Li, Aubrey
2020-10-26  9:01                 ` Peter Zijlstra
2020-10-27  3:17                   ` Li, Aubrey
2020-10-27 14:19                   ` Joel Fernandes
2020-10-27 15:23                     ` Joel Fernandes
2020-10-27 14:14                 ` Joel Fernandes
2020-10-20  1:43 ` [PATCH v8 -tip 03/26] sched: Core-wide rq->lock Joel Fernandes (Google)
2020-10-26 11:59   ` Peter Zijlstra
2020-10-27 16:27     ` Joel Fernandes
2020-10-20  1:43 ` [PATCH v8 -tip 04/26] sched/fair: Add a few assertions Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 05/26] sched: Basic tracking of matching tasks Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 06/26] sched: Add core wide task selection and scheduling Joel Fernandes (Google)
2020-10-23 13:51   ` Peter Zijlstra
2020-10-23 13:54     ` Peter Zijlstra
2020-10-23 17:57       ` Joel Fernandes
2020-10-23 19:26         ` Peter Zijlstra
2020-10-23 21:31           ` Joel Fernandes
2020-10-26  8:28             ` Peter Zijlstra
2020-10-27 16:58               ` Joel Fernandes
2020-10-26  9:31             ` Peter Zijlstra
2020-11-05 18:50               ` Joel Fernandes
2020-11-05 22:07                 ` Joel Fernandes
2020-10-23 15:05   ` Peter Zijlstra
2020-10-23 17:59     ` Joel Fernandes
2020-10-20  1:43 ` [PATCH v8 -tip 07/26] sched/fair: Fix forced idle sibling starvation corner case Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 08/26] sched/fair: Snapshot the min_vruntime of CPUs on force idle Joel Fernandes (Google)
2020-10-26 12:47   ` Peter Zijlstra
2020-10-28 15:29     ` Joel Fernandes
2020-10-28 18:39     ` Joel Fernandes
2020-10-29 16:59     ` Joel Fernandes
2020-10-29 18:24     ` Joel Fernandes
2020-10-29 18:59       ` Peter Zijlstra
2020-10-30  2:36         ` Joel Fernandes
2020-10-30  2:42           ` Joel Fernandes
2020-10-30  8:41             ` Peter Zijlstra
2020-10-31 21:41               ` Joel Fernandes
2020-10-20  1:43 ` [PATCH v8 -tip 09/26] sched: Trivial forced-newidle balancer Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 10/26] sched: migration changes for core scheduling Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 11/26] irq_work: Cleanup Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 12/26] arch/x86: Add a new TIF flag for untrusted tasks Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 13/26] kernel/entry: Add support for core-wide protection of kernel-mode Joel Fernandes (Google)
2020-10-20  3:41   ` Randy Dunlap
2020-11-03  0:20     ` Joel Fernandes
2020-10-22  5:48   ` Li, Aubrey
2020-11-03  0:50     ` Joel Fernandes
2020-10-30 10:29   ` Alexandre Chartre
2020-11-03  1:20     ` Joel Fernandes
2020-11-06 16:57       ` Alexandre Chartre
2020-11-06 17:43         ` Joel Fernandes
2020-11-06 18:07           ` Alexandre Chartre
2020-11-10  9:35       ` Alexandre Chartre
2020-11-10 22:42         ` Joel Fernandes
2020-11-16 10:08           ` Alexandre Chartre
2020-11-16 14:50             ` Joel Fernandes
2020-11-16 15:43               ` Joel Fernandes
2020-10-20  1:43 ` [PATCH v8 -tip 14/26] entry/idle: Enter and exit kernel protection during idle entry and exit Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 15/26] entry/kvm: Protect the kernel when entering from guest Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 16/26] sched: cgroup tagging interface for core scheduling Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 17/26] sched: Split the cookie and setup per-task cookie on fork Joel Fernandes (Google)
2020-11-04 22:30   ` chris hyser
2020-11-05 14:49     ` Joel Fernandes
2020-11-09 23:30     ` chris hyser
2020-10-20  1:43 ` [PATCH v8 -tip 18/26] sched: Add a per-thread core scheduling interface Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 19/26] sched: Add a second-level tag for nested CGroup usecase Joel Fernandes (Google)
2020-10-31  0:42   ` Josh Don
2020-11-03  2:54     ` Joel Fernandes
     [not found]   ` <6c07e70d-52f2-69ff-e1fa-690cd2c97f3d@linux.intel.com>
2020-11-05 15:52     ` Joel Fernandes
2020-10-20  1:43 ` [PATCH v8 -tip 20/26] sched: Release references to the per-task cookie on exit Joel Fernandes (Google)
2020-11-04 21:50   ` chris hyser
2020-11-05 15:46     ` Joel Fernandes
2020-10-20  1:43 ` [PATCH v8 -tip 21/26] sched: Handle task addition to CGroup Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 22/26] sched/debug: Add CGroup node for printing group cookie if SCHED_DEBUG Joel Fernandes (Google)
2020-10-20  1:43 ` [PATCH v8 -tip 23/26] kselftest: Add tests for core-sched interface Joel Fernandes (Google)
2020-10-30 22:20   ` [PATCH] sched: Change all 4 space tabs to actual tabs John B. Wyatt IV
2020-10-20  1:43 ` [PATCH v8 -tip 24/26] sched: Move core-scheduler interfacing code to a new file Joel Fernandes (Google)
2020-10-26  1:05   ` Li, Aubrey
2020-11-03  2:58     ` Joel Fernandes
2020-10-20  1:43 ` [PATCH v8 -tip 25/26] Documentation: Add core scheduling documentation Joel Fernandes (Google)
2020-10-20  3:36   ` Randy Dunlap
2020-11-12 16:11     ` Joel Fernandes
2020-10-20  1:43 ` [PATCH v8 -tip 26/26] sched: Debug bits Joel Fernandes (Google)
2020-10-30 13:26 ` [PATCH v8 -tip 00/26] Core scheduling Ning, Hongyu
2020-11-06  2:58   ` Li, Aubrey
2020-11-06 17:54     ` Joel Fernandes
2020-11-09  6:04       ` Li, Aubrey [this message]
2020-11-06 20:55 ` [RFT for v9] (Was Re: [PATCH v8 -tip 00/26] Core scheduling) Joel Fernandes
2020-11-13  9:22   ` Ning, Hongyu
2020-11-13 10:01     ` Ning, Hongyu

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