Re: Massive performance loss from OS::sleep hack

Kip Macy wrote:
Yes, if we could hack the jvm to work around this without calling
sleep that would be better yet. However, making java work well is more
important than keeping the interface clean.

One possible alternative is to not honor thread priorities in the
jdk by default. In hotspot/src/os/linux/vm/os_linux.cpp I see this
comment:

// Note: LinuxThreads only honor thread priority for real time threads.
// sched_priority is ignored if policy is SCHED_OTHER. This function is
// equivalent to a "noop" on current Linux platforms.
OSReturn os::set_native_priority(Thread* thread, int newpri) {

which leads me to believe linux doesn't honor thread priorities
in the jdk. Perhaps someone could verify that on a linux box.
If linux and/or windows doesn't actually honor thread priorities
I don't see why we need to.

IIRC, there weren't any specific JCK tests that validated a higher
priority thread actually got more time then a lower one (I could
be wrong on that since there was > 30k tests in the jck).

So we could default UseThreadPriorities to false and make the os_sleep()
call only be used when UseThreadPriorities is true (i.e. the user
explicitly sets -XX:+UseThreadPriorities).

Can someone check out linux to see if it indeed supports or ignores
thread priorities for java programs?

-Kurt
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