Re: [RFC/PATCH] FUSYN Realtime & robust mutexes for Linux, v2.3.1
From: Andrew Morton
Date: Thu Aug 05 2004 - 02:47:20 EST
Ulrich Drepper <drepper@xxxxxxxxxx> wrote:
> Andrew Morton wrote:
> > How large is the slowdown, and on what workloads?
> The fast path for all locking primitives etc in nptl today is entirely
> at userlevel. Normally just a single atomic operation with a dozen
> other instructions. With the fusyn stuff each and every locking
> operation needs a system call to register/unregister the thread as it
> locks/unlocks mutex/rwlocks/etc. Go figure how well this works. We are
> talking about making the fast path of the locking primitives
> two/three/four orders of magnitude more expensive. And this for
> absolutely no benefit for 99.999% of all the code which uses threads.
ouch, OK. But doesn't the current futex code continue to work unchanged?
> > Passing the lock to a non-rt task when there's an rt-task waiting for it
> > seems pretty poor form, too.
> No no, that's not what is wanted. Robust mutexes are a special kind of
> mutex and not related to rt issues.
I was referring to "scheduling-policy based unlock/wakeup", actually.
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