Date: Wed, 20 Dec 2000 11:03:48 +1030 From: Greg Lehey <grog@lemis.com> To: freebsd-hackers@FreeBSD.ORG Cc: "Jacques A. Vidrine" <n@nectar.com>, hackers@FreeBSD.ORG Subject: Optimizations (was: Why not another style thread? (was Re: cvs commit: src/lib/libc/gen getgrent.c)) Message-ID: <20001220110348.P43017@wantadilla.lemis.com> In-Reply-To: <20001219160152.E79058@dragon.nuxi.com>; from obrien@FreeBSD.ORG on Tue, Dec 19, 2000 at 04:01:52PM -0800 References: <20001217153129.B63080@hamlet.nectar.com> <20001217153656.F54486@holly.calldei.com> <20001217155648.C63080@hamlet.nectar.com> <20001217160442.H54486@holly.calldei.com> <20001217170316.A63227@hamlet.nectar.com> <200012180501.WAA87838@harmony.village.org> <20001218123108.A65143@hamlet.nectar.com> <200012181840.LAA92561@harmony.village.org> <20001218131112.B65143@hamlet.nectar.com> <20001219160152.E79058@dragon.nuxi.com>
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On Tuesday, 19 December 2000 at 16:01:52 -0800, David O'Brien wrote: > On Mon, Dec 18, 2000 at 01:11:12PM -0600, Jacques A. Vidrine wrote: >> /* Case 1 */ /* Case 2 */ >> if (data) vs. free(data) >> free(data); > > > Actually from an optimization standpoint, #1 can be worse (ie, harder on > the processor). You've got a conditional jump there that is using branch > prediction HW to track (which means there is some other conditional > branch you're not, you're fetching both the taken and not take paths, > etc... If the function call isn't expensive, #2 can be "faster". In which processors is a function call anywhere near as cheap as a conditional local branch? Greg -- Finger grog@lemis.com for PGP public key See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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