linux-kernel - Re: [RFC PATCH v2 6/8] cpuidle: make fast idle threshold tunable

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Date:   Tue, 17 Oct 2017 02:01:17 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     "Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:     Aubrey Li <aubrey.li@...el.com>, tglx@...utronix.de,
        peterz@...radead.org, len.brown@...el.com, ak@...ux.intel.com,
        tim.c.chen@...ux.intel.com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 6/8] cpuidle: make fast idle threshold tunable

On Monday, October 16, 2017 8:00:45 AM CEST Li, Aubrey wrote:
> On 2017/10/14 8:59, Rafael J. Wysocki wrote:
> > On Saturday, September 30, 2017 9:20:32 AM CEST Aubrey Li wrote:
> >> Add a knob to make fast idle threshold tunable
> >>
> >> Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com>
> > 
> > I first of all am not sure about the need to add a tunable for this at all
> > in the first place.
> 
> Actually I think a fixed value(10) might be good enough but not quite sure
> if there is a requirement to tune it for different scenario, for example even
> if the predicted idle interval is 100x overhead, I still want a fast path for
> a better benchmark score?

Any new tunables make the test matrix expand considerably, so it generally is
better to err on the conservative side with adding them.

Thanks,
Rafael