linux-kernel - Re: [RFC PATCH 07/11] sched: Add proxy execution

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Message-Id: <F34EC553-9C1E-4027-A4BB-BAA8D443235F@joelfernandes.org>
Date:   Mon, 17 Oct 2022 00:03:09 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Connor O'Brien <connoro@...gle.com>,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        John Stultz <jstultz@...gle.com>,
        Qais Yousef <qais.yousef@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>, youssefesmat@...gle.com
Subject: Re: [RFC PATCH 07/11] sched: Add proxy execution



> On Oct 16, 2022, at 4:48 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> On Sat, 15 Oct 2022 15:53:19 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
>>> 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..).
> 
> Does this mean that a lower priority task could do a sort of DOS attack
> on a high priority task, if it creates a bunch of threads that
> constantly grabs a shared lock from the higher priority task? That is,
> the higher priority task could possibly lose a lot of its quota due to
> other tasks running on its behalf in the critical section?

Just my opinion: I can see that as a problem, but on the other hand, if a bunch of threads are acquiring a shared lock to block a high priority task, then they are probably causing a DOS-type of issue anyway whether PE is enabled or not.  Even if a prio inheritance mechanism boosts them, they’re still making the progress of the blocking high priority tasks slower. Or, did I miss something in this use case?

Thanks.