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Date: Thu, 01 Nov 2007 10:40:39 -0400 From: Gregory Haskins <gregory.haskins.ml@...il.com> To: Nick Piggin <npiggin@...e.de> CC: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Andi Kleen <ak@...e.de>, Ingo Molnar <mingo@...e.hu> Subject: Re: [patch 1/4] x86: FIFO ticket spinlocks Nick Piggin wrote: > Introduce ticket lock spinlocks for x86 which are FIFO. The implementation > is described in the comments. The straight-line lock/unlock instruction > sequence is slightly slower than the dec based locks on modern x86 CPUs, > however the difference is quite small on Core2 and Opteron when working out of > cache, and becomes almost insignificant even on P4 when the lock misses cache. > trylock is more significantly slower, but they are relatively rare. > > On an 8 core (2 socket) Opteron, spinlock unfairness is extremely noticable, > with a userspace test having a difference of up to 2x runtime per thread, and > some threads are starved or "unfairly" granted the lock up to 1 000 000 (!) > times. After this patch, all threads appear to finish at exactly the same > time. I had observed this phenomenon on some 8-ways here as well, but I didn't have the bandwidth to code something up. Thumbs up! Regards, -Greg - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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