Date: Tue, 17 Feb 2015 11:12:22 -0500 From: Rich Felker <dalias@...c.org> To: Denys Vlasenko <vda.linux@...glemail.com> Cc: musl <musl@...ts.openwall.com> Subject: Re: [PATCH] x86_64/memset: use "small block" code for blocks up to 30 bytes long On Tue, Feb 17, 2015 at 02:08:52PM +0100, Denys Vlasenko wrote: > >> Please see attached file. > > > > I tried it and it's ~1 cycle slower for at least sizes 16-30; > > presumably we're seeing the cost of the extra compare/branch at these > > sizes but not at others. What does your timing test show? > > See below. > First column - result of my2.s > Second column - result of vda1.s > > Basically, the "rep stosq" code path got a bit faster, while > small memsets stayed the same. Can you post your test program for me to try out? Here's what I've been using, attached. Rich View attachment "memset-cycles.c" of type "text/plain" (1275 bytes)
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