Alexei, I've also heard that currently pthread mutexes are built on base of futexes for sake of performance. I don't know what's going on in EnterCriticalSection on Windows though. That's interesting... I'll measure the performance with some microbenchmark :)
Thanks, Aleksey. On Feb 13, 2008 3:38 AM, Alexei Fedotov <[EMAIL PROTECTED]> wrote: > Hello Aleksey, > Is not the current mutex implementation no less efficient than futex? > I've heard that mutexes try to spin before switching to kernel, and > Windows critical sections do the same trick. > > Thanks! > > > On Feb 13, 2008 2:12 AM, Aleksey Shipilev <[EMAIL PROTECTED]> wrote: > > Hi, Alexei, all, > > > > Just another idea for startup optimizations pops out of our talk with > > Egor Pasko. :) > > > > As you probably know there are many places in VM and JIT that use > > locking for safety reasons. Most of this locking is driven by mutexes, > > that is, the kernel calls. That's a good option in case of contention, > > because such locking will need arbitration (e.g. "who will take the > > mutex next"?) from kernel side. But what if that locking is not > > contended? Even then we will make the kernel call for trying to catch > > the mutex. > > > > Linux has long ago implemented such thing as "fast user-space mutex", > > "futex" [1]. Generally it is simple memory region that could be > > incremented/decremented atomically. In case of contention futex, of > > course, will resort to kernel-side mutex. > > > > That mean we could save precious time using futexes instead of > > mutexes: we definitely will save on kernel call time. > > > > AFAIK, current implementation of porting layer has no support for > > futexes even on Linux side. And so we might try to implement them for > > Windows part and use the Linux-provided futex'es on Linux part. Then > > after the implementation of hyfutex_lock/unlock we might try to > > migrate performance-significant locks to futexes one-by-one. Profilers > > are good directions, maybe anywhere else too. > > > > What do you think? > > > > Thanks, > > Aleksey, > > ESSD, Intel > > > > [1] http://en.wikipedia.org/wiki/Futex > > > > > > -- > With best regards, > Alexei >
