On Friday 30 November 2007 14:15, Zhang, Yanmin wrote: > On Fri, 2007-11-30 at 13:46 +1100, Nick Piggin wrote: > > On Wednesday 28 November 2007 09:57, Arjan van de Ven wrote:
> > > sounds like a bad idea; volanomark (well, technically the jvm behind > > > it) is abusing sched_yield() by assuming it does something it really > > > doesn't do, and as it happens some of the earlier 2.6 schedulers > > > accidentally happened to behave in a way that was nice for this > > > benchmark. > > > > OK, why is this still happening? Haven't we been asking JVMs to use > > futexes or posix locking for years and years now? Are there any sane > > jvms that _don't_ use yield? > > I think it's an issue of volanomark (a kind of java application) instead of > JVM. volanomark itself and not the jvm is calling sched_yield()? Do we have any non-toy threaded java apps? (what's JAVA in the kernel-perf tests?) > > > Todays kernel has a different behavior somewhat (and before people > > > scream "regression"; sched_yield() behavior isn't really specified and > > > doesn't make any sense at all, whatever you get is what you get.... > > > it's pretty much an insane defacto behavior that is incredibly tied to > > > which decisions the scheduler makes how, and no app can depend on that > > > > It is a performance regression. Is there any reason *not* to use the > > "compat" yield by default? > > There is no, so I suggest to set sched_compat_yield=1 by default. > If sched_compat_yield=0, kernel almost does nothing but returns. When > sched_compat_yield=1, it is closer to the meaning of sched_yield man page. sched_yield() is really only defined for posix realtime scheduling AFAIK, which talks about priority lists. SCHED_OTHER is defined to be a single priority, below the rest of the realtime priorities. So at first you *might* say that the process should then be made to run only after all other SCHED_OTHER processes, however there is no such ordering requirement for SCHED_OTHER scheduling. The SCHED_OTHER scheduler can run any task at any time. That said, I think people would *expect* that call be much closer to the compat behaviour than the current default. And that's definitely what Linux has done in the past. So there really does need to be a good reason to change it like this IMO. > > As you say, for SCHED_OTHER tasks, yield > > can do almost anything. We may as well do something that isn't a > > regression... > > I just found SCHED_OTHER in man sched_setscheduler. Is it SCHED_NORMAL in > the latest kernel? Yes, SCHED_NORMAL is SCHED_OTHER. Don't know why it got renamed... - 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/
