Date: Sat, 13 Apr 2013 16:55:38 +0200
From: Stanislaw Gruszka <sgruszka@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-tip-commits@vger.kernel.org
Subject: Re: [tip:sched/core] sched: Lower chances of cputime scaling overflow
Message-ID: <20130413145538.GB11556@redhat.com>
References: <tip-d9a3c9823a2e6a543eb7807fb3d15d8233817ec5@git.kernel.org>
 <20130326140147.GB2029@redhat.com>
 <1365687946.8824.3.camel@laptop>
 <CA+55aFway4C89fTewKvED4RvFLaNdM-BVtkJ2YChsvracLKiyA@mail.gmail.com>
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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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