linux-kernel - Re: [RFC PATCH v2 7/7] sched/idle: update poll time when wakeup from idle

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Message-ID: <20170829124655.ann5cipoubl5lppn@hirez.programming.kicks-ass.net>
Date:   Tue, 29 Aug 2017 14:46:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yang Zhang <yang.zhang.wz@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        wanpeng.li@...mail.com, mst@...hat.com, pbonzini@...hat.com,
        tglx@...utronix.de, rkrcmar@...hat.com, dmatlack@...gle.com,
        agraf@...e.de, linux-doc@...r.kernel.org,
        Quan Xu <quan.xu0@...il.com>, Ingo Molnar <mingo@...hat.com>
Subject: Re: [RFC PATCH v2 7/7] sched/idle: update poll time when wakeup from
 idle

On Tue, Aug 29, 2017 at 11:46:41AM +0000, Yang Zhang wrote:
> In ttwu_do_wakeup, it will update avg_idle when wakeup from idle. Here
> we just reuse this logic to update the poll time. It may be a little
> late to update the poll in ttwu_do_wakeup, but the test result shows no
> obvious performance gap compare with updating poll in irq handler.
> 
> one problem is that idle_stamp only used when using CFS scheduler. But
> it is ok since it is the default policy for scheduler and only consider
> it should enough.
> 
> Signed-off-by: Yang Zhang <yang.zhang.wz@...il.com>
> Signed-off-by: Quan Xu <quan.xu0@...il.com>

Same broken SoB chain, and not a useful word on why you need to adjust
this crap to begin with. What you want that poll duration to be related
to is the cost of a VMEXIT/VMENTER cycle, not however long we happened
to be idle.

So no.