* Jarek Poplawski <[EMAIL PROTECTED]> wrote: > > the (small) patch below fixes the iperf locking bug and removes the > > yield() use. There are numerous immediate benefits of this patch: > ... > > > > sched_yield() is almost always the symptom of broken locking or other > > bug. In that sense CFS does the right thing by exposing such bugs =B-) > > ...Only if it were under some DEBUG option. [...]
note that i qualified my sentence both via "In that sense" and via a smiley! So i was not suggesting that this is a general rule at all and i was also joking :-) > [...] Even if iperf is doing the wrong thing there is no explanation > for such big difference in the behavior between sched_compat_yield 1 > vs. 0. It seems common interfaces should work similarly and > predictably on various systems, and here, if I didn't miss something, > linux looks like a different kind? What you missed is that there is no such thing as "predictable yield behavior" for anything but SCHED_FIFO/RR tasks (for which tasks CFS does keep the behavior). Please read this thread on lkml for a more detailed background: CFS: some bad numbers with Java/database threading [FIXED] http://lkml.org/lkml/2007/9/19/357 http://lkml.org/lkml/2007/9/19/328 in short: the yield implementation was tied to the O(1) scheduler, so the only way to have the exact same behavior would be to have the exact same core scheduler again. If what you said was true we would not be able to change the scheduler, ever. For something as vaguely defined of an API as yield, there's just no way to have a different core scheduler and still behave the same way. So _generally_ i'd agree with you that normally we want to be bug for bug compatible, but in this specific (iperf) case there's just no point in preserving behavior that papers over this _clearly_ broken user-space app/thread locking (for which now two fixes exist already, plus a third fix is the twiddling of that sysctl). Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
