On Wednesday 28 November 2007 09:57, Arjan van de Ven wrote: > On Tue, 27 Nov 2007 17:33:05 +0800 > > "Zhang, Yanmin" <[EMAIL PROTECTED]> wrote: > > If echo "1">/proc/sys/kernel/sched_compat_yield before starting > > volanoMark testing, the result is very good with kernel 2.6.24-rc3 on > > my 16-core tigerton. > > > > 1) If /proc/sys/kernel/sched_compat_yield=1, comparing with 2.6.22, > > 2.6.24-rc3 has more than 70% improvement; > > 2) If /proc/sys/kernel/sched_compat_yield=0, comparing with 2.6.22, > > 2.6.24-rc3 has more than 80% regression; > > > > On other machines, the volanoMark result also has much improvement if > > /proc/sys/kernel/sched_compat_yield=1. > > > > Would you like to change function yield_task_fair to delete codes > > around sysctl_sched_compat_yield, or just initiate it to 1? > > 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? > 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? As you say, for SCHED_OTHER tasks, yield can do almost anything. We may as well do something that isn't a regression... > in any way. In fact, I've proposed to make sched_yield() just do an > msleep(1)... that'd be closer to what sched_yield is supposed to do > standard wise than any of the current behaviors .... ;_ What makes you say that? IIRC of all the things that sched_yeild can do, it is not allowed to block. So this is about the only thing that will break the standard... - 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/
