linux-kernel - Re: [PATCH v8 4/5] locking/qspinlock: Introduce starvation avoidance into CNA

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Date:   Thu, 30 Jan 2020 17:05:28 -0500
From:   Alex Kogan <alex.kogan@...cle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Waiman Long <longman@...hat.com>, linux@...linux.org.uk,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, hpa@...or.com, x86@...nel.org,
        Hanjun Guo <guohanjun@...wei.com>,
        Jan Glauber <jglauber@...vell.com>,
        Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        dave.dice@...cle.com
Subject: Re: [PATCH v8 4/5] locking/qspinlock: Introduce starvation avoidance
 into CNA


> On Jan 25, 2020, at 6:19 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Fri, Jan 24, 2020 at 01:19:05PM -0500, Alex Kogan wrote:
> 
>> Is there a lightweight way to identify such a “prioritized” thread?
> 
> No; people might for instance care about tail latencies between their
> identically spec'ed worker tasks.

I would argue that those users need to tune/reduce the intra-node handoff
threshold for their needs. Or disable CNA altogether.

In general, Peter, seems like you are not on board with the way Longman
suggested to handle prioritized threads. Am I right?

Thanks,
— Alex