Date: Tue, 23 Mar 2004 17:24:45 -0500 From: John Baldwin <jhb@FreeBSD.org> To: des@des.no (Dag-Erling =?utf-8?q?Sm=C3=B8rgrav?=) Cc: Seigo Tanimura <tanimura@tanimura.dyndns.org> Subject: Re: Is MTX_CONTESTED evil? Message-ID: <200403231724.45923.jhb@FreeBSD.org> In-Reply-To: <xzpekrjtjj7.fsf@dwp.des.no> References: <200403160519.i2G5J0V6023193@urban> <xzplllrtjm0.fsf@dwp.des.no> <xzpekrjtjj7.fsf@dwp.des.no>
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On Tuesday 23 March 2004 03:06 pm, Dag-Erling Smørgrav wrote: > des@des.no (Dag-Erling Smørgrav) writes: > > John Baldwin <john@baldwin.cx> writes: > > > Adaptive mutexes work just fine, but they aren't on by default. > > > > No, they don't "work just fine", unless of course they are *supposed* > > to cause frequent panics. > > s/panic/freeze/ They worked just fine on sparc64, alpha, and i386 when they were developed and nothing has changed since then. However, since they increase the chances of "near concurrency" on multiple CPUs (i.e. one CPU grabbing a lock right after another released it) they expose races and thus bugs in code that uses mutexes improperly. The fault is not in adaptive mutexes, but in the other broken code, just as compile failures aren't the result of the tinderbox itself being broken. :-) -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.orghome | help
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