From mboxrd@z Thu Jan 1 00:00:00 1970 From: Davide Libenzi Date: Sat, 24 May 2003 00:20:13 +0000 Subject: RE: [Linux-ia64] Re: web page on O(1) scheduler Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org On Fri, 23 May 2003, Boehm, Hans wrote: > Pthread_spin_lock() under the NPTL version in RH9 does basically what my > custom locks do in the uncontested case, aside from the function call. > But remember that this began with a discussion about whether it was > reasonable for user locking code to explicitly yield rather than relying > on pthreads to suspend the thread. I don't think pthread_spin_lock is > relevant in this context, for two reasons: > > 1) At least the RH9 version of pthread_spin_lock in NPTL literally spins > and makes no attempt to yield or block. This only makes sense at user > level if you are 100% certain that the processors won't be > overcommitted. Otherwise there is little to be lost by blocking once you > have spun for sufficiently long. You could use pthread_spin_trylock and > block explicitly, but that gets us back to custom blocking code. Yes, that would be a spinlock. Your code was basically a spinlock that instead of spinning was doing abort() in contention case. Again, you measured two different things. Even if the pthread mutex does something very simple like : spinlock(mtx->lock); while (mtx->busy) { spinunlock(mtx->lock); waitforunlocks(); spinlock(mtx->lock); } mtx->busy++; spinunlock(mtx->lock); Only the fact that this code likely reside inside a deeper call lever will make you pay in a tight loop like your. > 2) AFAICT, pthread_spin_lock is currently a little too bleeding edge to > be widely used. I tried to time it, but failed. Pthread.h doesn't > include the declaration for pthread_spin_lock_t by default, at least not > yet. It doesn't seem to have a Linux man page, yet. I tried to define > the magic macro to get it declared, but that broke something else. $ gcc -D_GNU_SOURCE ... - Davide