linux-kernel - Re: [tip:sched/core] sched: Lower chances of cputime scaling overflow

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Message-ID: <20130413145538.GB11556@redhat.com>
Date:	Sat, 13 Apr 2013 16:55:38 +0200
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched: Lower chances of cputime scaling overflow

On Thu, Apr 11, 2013 at 08:38:37AM -0700, Linus Torvalds wrote:
>     /* We know one of the values has a bit set in the high 32 bits */
>     for (;;) {
>         /* Make sure "stime" is the bigger of stime/rtime */
>         if (rtime > stime) {
>             u64 tmp = stime; stime = rtime; rtime = tmp;
>         }

For most workloads rtime is bigger than stime, so swapping those would
save some cycles on common cases. Otherwise this algorithm looks great.

Thanks
Stanislaw

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