linux-kernel - Re: [PATCH v1 0/2] cpuidle: teo: Refine handling of short idle intervals

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Message-ID: <23742d13848a8cdf24da43c08ebe061211f46ecc.camel@linux.ibm.com>
Date: Mon, 14 Apr 2025 12:45:20 +0530
From: Aboorva Devarajan <aboorvad@...ux.ibm.com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM
 <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
        Daniel Lezcano	
 <daniel.lezcano@...aro.org>,
        Christian Loehle <christian.loehle@....com>,
        Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
        Doug Smythies
 <dsmythies@...us.net>
Subject: Re: [PATCH v1 0/2] cpuidle: teo: Refine handling of short idle
 intervals

On Thu, 2025-04-03 at 21:16 +0200, Rafael J. Wysocki wrote:
> Hi Everyone,
> 
> This series is intended to address an issue with overly aggressive selection
> of idle state 0 (the polling state) in teo on x86 in some cases when timer
> wakeups dominate the CPU wakeup pattern.
> 
> In those cases, timer wakeups are not taken into account when they are
> within the LATENCY_THRESHOLD_NS range and the idle state selection may
> be based entirely on non-timer wakeups which may be rare.  This causes
> the prediction accuracy to be low and too much energy may be used as
> a result.
> 
> The first patch is preparatory and it is not expected to make any
> functional difference.
> 
> The second patch causes teo to take timer wakeups into account if it
> is about to skip the tick_nohz_get_sleep_length() invocation, so they
> get a chance to influence the idle state selection.
> 
> I have been using this series on my systems for several weeks and observed
> a significant reduction of the polling state selection rate in multiple
> workloads.
> 
> Thanks!
> 
> 

Hi Rafael,

I'm running some tests and going through the patch.
I haven't noticed any deviations so far, will post the results shortly.

Thanks,
Aboorva