linux-kernel - Re: [PATCH] sched: remove sched_find_first

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Date:   Tue, 16 May 2017 10:30:42 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Yury Norov <ynorov@...iumnetworks.com>
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Akinobu Mita <mita@...aclelinux.com>,
        Mike Galbraith <efault@....de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] sched: remove sched_find_first_bit()


* Yury Norov <ynorov@...iumnetworks.com> wrote:

> I collected about 700 results in dmesg, and took 600 fastest.
> For the vanilla kernel, the average value is 368, and for patched
> kernel it is 388. It's 5% slower. But the standard deviation is 
> really big for both series' - 131 and 106 cycles respectively, which
> is ~ 30%. And so, my conclusion is: there's no benefit in using
> sched_find_first_bit() comparing to find_first_bit().

Erm, so you in essence claim:

	"according to measurements the new code is 5% slower, with a high, 30% 
	 stddev, hence the new code is better!"

Basic logic fail...

Thanks,

	Ingo