Re: [PATCH] sched: recover sched_yield task running time increase

["Alex,Shi" <alex.shi@intel.com>]

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..."