linux-kernel - Re: [PATCH resend5 4/4] cputime: optimize jiffies_to

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Date:	Wed, 3 Jun 2009 15:06:57 +0200
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Mackerras <paulus@...ba.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH resend5 4/4] cputime: optimize jiffies_to_cputime(1)

Hi.

> > This patch (with 3 previous) was compiled on x86, x86_64, ppc with
> > CONFIG_VIRT_CPU_ACCOUNTNG=n, ppc64 with CONFIG_VIRT_CPU_ACCOUNTING=y.
> > Run time testing was done only on x86.

I tested patches on ppc64 with CONFIG_VIRT_CPU_ACCOUNTING=y . Additionally I
measure impact of iffies_to_cputime(1) to cputime_one_jiffiy conversion on
check_cpu_itimer() calls with below code:

+       xstart = get_cycles();
+       barrier();
        check_cpu_itimer(tsk, &sig->it[CPUCLOCK_PROF], &prof_expires, ptime,
                         SIGPROF);
        check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT], &virt_expires, utime,
                         SIGVTALRM);
+       barrier();
+       xend = get_cycles();
+       check_cpu_itimer_cycles += xend - xstart;
+       check_cpu_itimer_n++;

Using cputime_one_jiffy was about 4% faster.

Cheers
Stanislaw
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