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Subject: Re: [PATCH v3 0/5] Improve newidle lb cost tracking and early abort
From:   Tim Chen <tim.c.chen@linux.intel.com>
To:     Vincent Guittot <vincent.guittot@linaro.org>
Cc:     mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, linux-kernel@vger.kernel.org
Date:   Thu, 28 Oct 2021 14:36:08 -0700
In-Reply-To: <20211028121530.GA19512@vingu-book>
References: <20211019123537.17146-1-vincent.guittot@linaro.org>
         <7128695d64e9161637b67315b5beb51c4accdc82.camel@linux.intel.com>
         <CAKfTPtAv7vPGYAwUSmGL5wtbY=if8G+3geWMKpHu3vLGqthPfg@mail.gmail.com>
         <720fd26424927dd27fea4e5719dafe8a0afaa8c4.camel@linux.intel.com>
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On Thu, 2021-10-28 at 14:15 +0200, Vincent Guittot wrote:
> 
> > It seems to make sense to skip the call
> > to nohz_newidle_balance() for this case? 
> 
> nohz_newidle_balance() also tests this condition :
> (this_rq->avg_idle < sysctl_sched_migration_cost)
> and doesn't set NOHZ_NEWILB_KICKi in such case
> 
> But this patch now used the condition :
> this_rq->avg_idle < sd->max_newidle_lb_cost
> and sd->max_newidle_lb_cost can be higher than
> sysctl_sched_migration_cost
> 
> which means that we can set NOHZ_NEWILB_KICK:
> -although we decided to skip newidle loop
> -or when we abort because this_rq->avg_idle < curr_cost + sd-
> >max_newidle_lb_cost 
> 
> This is even more true when sysctl_sched_migration_cost is lowered
> which is your case IIRC
> 
> The patch below ensures that we don't set NOHZ_NEWILB_KICK in such
> cases:
> 

Thanks. Will ask our benchmark team to give it a spin.

Tim