Date: Fri, 15 Dec 2000 07:08:25 -0700 From: Chuck Paterson <cp@bsdi.com> To: Julian Elischer <julian@elischer.org> Cc: smp@FreeBSD.ORG Subject: Re: atomic increment? Message-ID: <200012151408.eBFE8PF44272@berserker.bsdi.com> In-Reply-To: Your message of "Fri, 15 Dec 2000 02:56:26 PST." <3A39F8DA.FD4CA0A5@elischer.org>
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Julian, This is not an argument against, or for, your request. I am sure I am starting to sound like a broken record, but so be it. Please remember that atomic ops are really expensive, at least as expensive as acquiring a mutex. In some cases, of which X86 is not one, they are more expensive than just acquiring the mutex. Typically they are cheaper than acquiring and releasing a mutex, in the case of X86 about half the cost. So, if there are more than two atomic operations and they could have been protected by a single mutex, then the single mutex really is slightly better alternative. At three operations the mutex is a much better alternative. This is not an argument against, or for, your request. Chuck Julian Elischer wrote on: Fri, 15 Dec 2000 02:56:26 PST }CAn we have an atomic increment and decrement primative? } }presently we get: } }.L565: } movl $1,%eax }#APP } lock } addl %eax,4(%ebx) } } }the movl is totally useless and it would be }an absolutly trivial addition.. }the question is; }is there a religious reason we don't already have it? }-- } __--_|\ Julian Elischer } / \ julian@elischer.org } ( OZ ) World tour 2000 }---> X_.---._/ presently in: Budapest } v } } }To Unsubscribe: send mail to majordomo@FreeBSD.org }with "unsubscribe freebsd-smp" in the body of the message To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-smp" in the body of the message
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