Messages in this thread | | | Subject | Re: [PATCH] sched: recover sched_yield task running time increase | From | Mike Galbraith <> | Date | Wed, 06 Apr 2011 09:01:29 +0200 |
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On Wed, 2011-04-06 at 14:15 +0800, Alex,Shi wrote: > On Wed, 2011-04-06 at 13:07 +0800, Rik van Riel wrote: > > On 04/05/2011 06:33 PM, Alex Shi wrote: > > > commit ac53db596cc08ecb8040c removed the sched_yield task running > > > time increase, so the yielded task get more opportunity to be launch > > > again. That may not the caller want to be. And this also causes > > > volano benchmark drop 50~80 percent performance on core2/NHM/WSM > > > machines. This patch recover the sched_yield task vruntime up. > > > > > > Signed-off-by: alex.shi@intel.com > > > > NACK > > > > This was switched off by default and under > > the sysctl sched_compat_yield for a reason. > > > > Reintroducing it under that sysctl option > > may be acceptable, but by default it would > > be doing the wrong thing for other workloads. > > I can implement this as sysctl option. But when I checked again the man > page of sched_yield. I have some concerns on this. > > ---- > int sched_yield(void); > > DESCRIPTION > A process can relinquish the processor voluntarily without blocking by calling sched_yield(). > The process will then be moved to the end of the queue for its static priority and a new process > gets to run. > ---- > > If a application calls sched_yield system call, most of time it is not > want to be launched again right now. so the man page said "the caller > process will then be moved to the _end_ of the queue..."
Moving a yielding nice 0 task behind a SCHED_IDLE (or nice 19) task could be incredibly painful.
-Mike
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