linux-kernel - Re: [RFC PATCH 09/16] sched/fair: core wide cfs task priority comparison(Internet mail)

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Message-ID: <20200724071458.lah33iacywx35hdi@aaronlu-desktop>
Date:   Fri, 24 Jul 2020 15:14:58 +0800
From:   Aaron Lu <aaron.lwe@...il.com>
To:     benbjiang(蒋彪) <benbjiang@...cent.com>
Cc:     Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "pjt@...gle.com" <pjt@...gle.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "subhra.mazumdar@...cle.com" <subhra.mazumdar@...cle.com>,
        "fweisbec@...il.com" <fweisbec@...il.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "kerrnel@...gle.com" <kerrnel@...gle.com>,
        Phil Auld <pauld@...hat.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        "vineethrp@...il.com" <vineethrp@...il.com>,
        Chen Yu <yu.c.chen@...el.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Aaron Lu <ziqian.lzq@...fin.com>
Subject: Re: [RFC PATCH 09/16] sched/fair: core wide cfs task priority
 comparison(Internet mail)

On Wed, Jul 22, 2020 at 12:23:44AM +0000, benbjiang(蒋彪) wrote:
> 
> 
> > +/*
> > + * This function takes care of adjusting the min_vruntime of siblings of
> > + * a core during coresched enable/disable.
> > + * This is called in stop machine context so no need to take the rq lock.
> Hi,
> 
> IMHO, it seems that stop machine context cannot guarantee race free. The param *cpu* maybe not *this_cpu*, rq lock should be taken even in stop machine context, and irq should be disabled too, to avoid potential races with other contexts.
> 

In stop machine context, all CPUs except the active ones are spinning
with irq disabled and in this invocation of stop_machine(), only one
CPU is active so I don't think race is possible.