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 Sm=C3=B8rgrav wrote: > des@des.no (Dag-Erling Sm=C3=B8rgrav) 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=20 nothing has changed since then. However, since they increase the chances o= f=20 "near concurrency" on multiple CPUs (i.e. one CPU grabbing a lock right aft= er=20 another released it) they expose races and thus bugs in code that uses=20 mutexes improperly. The fault is not in adaptive mutexes, but in the other= =20 broken code, just as compile failures aren't the result of the tinderbox=20 itself being broken. :-) =2D-=20 John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" =3D http://www.FreeBSD.org
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