linux-kernel - Re: [PATCH v2] cpuidle: poll_state: Add time limit to poll

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Message-ID: <20180322191127.GY4043@hirez.programming.kicks-ass.net>
Date:   Thu, 22 Mar 2018 20:11:27 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Rik van Riel <riel@...riel.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Thomas Ilsche <thomas.ilsche@...dresden.de>,
        Doug Smythies <dsmythies@...us.net>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Mike Galbraith <mgalbraith@...e.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] cpuidle: poll_state: Add time limit to poll_idle()

On Thu, Mar 22, 2018 at 12:32:18PM -0400, Rik van Riel wrote:
> On Wed, 2018-03-14 at 13:04 +0100, Peter Zijlstra wrote:
> 
> > On x86 we don't have to use that time_check_counter thing,
> > sched_clock()
> > is really cheap, not sure if it makes sense on other platforms.
> 
> Are you sure? I saw a 5-10% increase in CPU use,
> for a constant query rate to a memcache style
> workload, with v3 of this patch.

Well, I expected it to be really cheap, but if you have numbers saying
otherwise, clearly I'll need to adjust expectations ;-)