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From: Peter Zijlstra <peterz@infradead.org>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Connor O'Brien <connoro@google.com>,
	linux-kernel@vger.kernel.org, kernel-team@android.com,
	John Stultz <jstultz@google.com>,
	Qais Yousef <qais.yousef@arm.com>, Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	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>,
	Will Deacon <will@kernel.org>, Waiman Long <longman@redhat.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	youssefesmat@google.com
Subject: Re: [RFC PATCH 07/11] sched: Add proxy execution
Date: Sat, 15 Oct 2022 15:53:19 +0200	[thread overview]
Message-ID: <Y0q7TyEWco/PfOAI@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <Y0YeUhDZWb49mpLo@google.com>

On Wed, Oct 12, 2022 at 01:54:26AM +0000, Joel Fernandes wrote:

> Here, for CFS, doesn't this mean that the ->vruntime of the blocked task does
> not change while it is giving the owner a chance to run?
> 
> So that feels like if the blocked task is on the left-most node of the cfs
> rbtree, then it will always proxy to the owner while not letting other
> unrelated CFS tasks to run. That sounds like a breakage of fairness.
> 
> Or did I miss something?

So CFS will pick the leftmost task, if it happens to be the lock owner,
it will run as normal, owner time will advance.

When owner time is advanced enough to not be elegible anymore, it is
likely a blocked task is selected, at which time we'll advance it's
vruntime.

All this repeats until the whole block chain has advanced enough to make
the owner elegible again and the whole thing repeats.

From this it is easy to see that the critical secion executes with the
direct sum of the blockchain as a whole (all of them will have donated
their relative time to make the owner elegible again) -- provided the
critical section is of course long enough for this to matter (or it's
owner's weight small enough etc..).


  parent reply	other threads:[~2022-10-15 13:53 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-03 21:44 [RFC PATCH 00/11] Reviving the Proxy Execution Series Connor O'Brien
2022-10-03 21:44 ` [RFC PATCH 01/11] locking/ww_mutex: Remove wakeups from under mutex::wait_lock Connor O'Brien
2022-10-04 16:01   ` Waiman Long
2022-10-12 23:54     ` Joel Fernandes
2022-10-20 18:43     ` Connor O'Brien
2022-10-03 21:44 ` [RFC PATCH 02/11] locking/mutex: Rework task_struct::blocked_on Connor O'Brien
2022-10-03 21:44 ` [RFC PATCH 03/11] kernel/locking: Add p->blocked_on wrapper Connor O'Brien
2022-10-03 21:44 ` [RFC PATCH 04/11] locking/mutex: make mutex::wait_lock irq safe Connor O'Brien
2022-10-13  4:30   ` Joel Fernandes
2022-10-03 21:44 ` [RFC PATCH 05/11] sched: Split scheduler execution context Connor O'Brien
2022-10-14 17:01   ` Joel Fernandes
2022-10-19 17:17   ` Valentin Schneider
2022-10-20 18:43     ` Connor O'Brien
2022-10-03 21:44 ` [RFC PATCH 06/11] kernel/locking: Expose mutex_owner() Connor O'Brien
2022-10-03 21:44 ` [RFC PATCH 07/11] sched: Add proxy execution Connor O'Brien
2022-10-12  1:54   ` Joel Fernandes
2022-10-12  9:46     ` Juri Lelli
2022-10-14 17:07     ` Joel Fernandes
2022-10-15 13:53     ` Peter Zijlstra [this message]
2022-10-16 20:48       ` Steven Rostedt
2022-10-17  4:03         ` Joel Fernandes
2022-10-17  7:26         ` Peter Zijlstra
2022-10-24 22:33           ` Qais Yousef
2022-10-25 11:19             ` Joel Fernandes
2022-10-25 22:10               ` Qais Yousef
2022-10-15 15:28     ` Peter Zijlstra
2022-10-15 15:08   ` Peter Zijlstra
2022-10-15 15:10   ` Peter Zijlstra
2022-10-15 15:47   ` Peter Zijlstra
2022-10-24 10:13   ` Dietmar Eggemann
2022-10-29  3:31     ` Joel Fernandes
2022-10-31 16:39       ` Dietmar Eggemann
2022-10-31 18:00         ` Joel Fernandes
2022-11-04 17:09           ` Dietmar Eggemann
2022-11-21  0:22             ` Joel Fernandes
2022-11-21  1:49               ` Joel Fernandes
2022-11-21  3:59                 ` Joel Fernandes
2022-11-22 18:45                   ` Joel Fernandes
2023-01-09  8:51   ` Chen Yu
2022-10-03 21:44 ` [RFC PATCH 08/11] sched: Fixup task CPUs for potential proxies Connor O'Brien
2022-10-03 21:44 ` [RFC PATCH 09/11] sched/rt: Fix proxy/current (push,pull)ability Connor O'Brien
2022-10-10 11:40   ` Valentin Schneider
2022-10-14 22:32     ` Connor O'Brien
2022-10-19 17:05       ` Valentin Schneider
2022-10-20 13:30         ` Juri Lelli
2022-10-20 16:14           ` Valentin Schneider
2022-10-21  2:22         ` Connor O'Brien
2022-10-03 21:45 ` [RFC PATCH 10/11] torture: support randomized shuffling for proxy exec testing Connor O'Brien
2022-11-12 16:54   ` Joel Fernandes
2022-11-14 20:44     ` Connor O'Brien
2022-11-15 16:02       ` Joel Fernandes
2022-10-03 21:45 ` [RFC PATCH 11/11] locktorture: support nested mutexes Connor O'Brien
2022-10-06  9:59 ` [RFC PATCH 00/11] Reviving the Proxy Execution Series Juri Lelli
2022-10-06 10:07   ` Peter Zijlstra
2022-10-06 12:14     ` Juri Lelli
2022-10-15 15:44 ` Peter Zijlstra
2022-10-17  2:23 ` Joel Fernandes
2022-10-19 11:43   ` Qais Yousef
2022-10-19 12:23     ` Joel Fernandes
2022-10-19 13:41       ` Juri Lelli
2022-10-19 13:51         ` Joel Fernandes
2022-10-19 19:30         ` Qais Yousef
2022-10-20  8:51           ` Joel Fernandes
2022-10-17  3:25 ` Chengming Zhou
2022-10-17  3:56   ` Joel Fernandes
2022-10-17  4:26     ` Chengming Zhou
2022-10-17 12:27       ` Joel Fernandes

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