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

[Rik van Riel <riel@redhat.com>]

On 04/06/2011 04:04 AM, Peter Zijlstra wrote:
> On Wed, 2011-04-06 at 06:33 +0800, 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.
>
> You do know that any app that relies on sched_yield behaviour is more
> than broken? Using sched_yield() for anything other than SCHED_FIFO
> tasks is well outside spec.
>
> Furthermore, apparently you used sysctl_sched_compat_yield, which was
> bound to disappear some time, since with the default settings the yield
> semantics didn't actually change.
>
> So no, I'm not much inclined to accept this. The Java people have had
> every opportunity to go fix their crap, them not doing so will
> eventually (preferably now) stop being my problem.

It appears they might not have figured out how to fix
their stuff :)

Would you have any hints on what the Java folks should
replace their calls to sched_yield with?

Proper use of futexes from inside the JVM perhaps?

Or should we export yield_to to userspace and have
them use that? :)   *runs*