Re: Spinlocks, yet again: analysis and proposed patches

Greg Stark <gsstark@mit.edu> writes:

> Tom Lane <tgl@sss.pgh.pa.us> writes:
>
>> No; that page still says specifically "So a process calling
>> sched_yield() now must wait until all other runnable processes in the
>> system have used up their time slices before it will get the processor
>> again."  I can prove that that is NOT what happens, at least not on
>> a multi-CPU Opteron with current FC4 kernel.  However, if the newer
>> kernels penalize a process calling sched_yield as heavily as this page
>> claims, then it's not what we want anyway ...
>
> Well it would be no worse than select or any other random i/o syscall.
>
> It seems to me what you've found is an outright bug in the linux scheduler.
> Perhaps posting it to linux-kernel would be worthwhile.

People have complained on l-k several times about the 2.6
sched_yield() behavior; the response has basically been "if you rely
on any particular sched_yield() behavior for synchronization, your app
is broken--it's not a synchronization primitive."

-Doug