Messages in this thread |  | | | Date | Wed, 15 Feb 2012 08:37:10 -0600 | | From | Dimitri Sivanich <> | | Subject | Re: [PATCH] specific do_timer_cpu value for nohz off mode |
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On Wed, Feb 15, 2012 at 03:16:34PM +0100, Thomas Gleixner wrote: > On Tue, 8 Nov 2011, Dimitri Sivanich wrote: > > > > Allow manual override of the tick_do_timer_cpu. > > > > While not necessarily harmful, doing jiffies updates on an application cpu > > does cause some extra overhead that HPC benchmarking people notice. They > > prefer to have OS activity isolated to certain cpus. They like reproducibility > > of results, and having jiffies updates bouncing around introduces variability. > > I really wonder about this changelog. The only case where jiffies > updates bounces around is the NOHZ case. In all other modes (periodic > or highres) the boot cpu gets the do_timer() duty and it's never > assigned to any other cpu. > > So what's the point of this exercise? Moving it away from CPU0 for > acedemic reasons or what? > I wasn't specifically trying to move it away from CPU0 (having jiffies updates on CPU0 was and would be just fine for the nohz=off case). The issue was that the tick_do_timer_cpu could be any cpu even in the nohz=off case (maybe something has changed that since?). After the point of assignment it is static, but you never know which cpu it is.
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