Date: Mon, 16 Apr 2001 14:30:52 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp> Cc: bright@wintelcom.net, dillon@earth.backplane.com, riel@conectiva.com.br, bsddiy@21cn.com, Tor.Egge@fast.no, freebsd-hackers@FreeBSD.ORG Subject: Re: vm balance Message-ID: <2033.987424252@critter> In-Reply-To: Your message of "Mon, 16 Apr 2001 21:23:34 %2B0900." <200104161223.f3GCNZZ51680@rina.r.dl.itc.u-tokyo.ac.jp>
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In message <200104161223.f3GCNZZ51680@rina.r.dl.itc.u-tokyo.ac.jp>, Seigo Tanim ura writes: >Poul-Henning> I'm a bit worried about the amount of work done in the >Poul-Henning> cache_purgeleafdirs(), considering how often it is called, > >Poul-Henning> Do you have measured the performance impact of this to be an >Poul-Henning> insignificant overhead ? > >No precise results right now, mainly because I cannot find a benchmark >to measure the performance of name lookup going down to a deep >directory depth. Have you done any "trivial" checks, like timing "make world" and such ? >It has been confirmed, though, that the hit ratio of name lookup is >around 96-98% for a box serving cvsup both with and without my patch >(observed by systat(1)). Here are the details of the name lookup on >that box: Ohh, sure, I don't expect this to have a big impact on the hit rate, If I thought it would have I would have protested :-) >For a more precise investigation, we have to measure the actial time >taken for a lookup operation, in which case I may have to write a >benchmark for it and test in single-user mode. I would be satisfied with a "sanity-check", for instance running a "cvs co src ; cd src ; make buildworld ; cd release ; make release" with and without, just to see that it doesn't have a significant negative impact. >It is interesting that the hit ratio of directory lookup is up to only >1% at most, even without my patch. Why is it like that? Uhm, which cache is this ? The one reported in "vmstat -vm" ? That is entirely different from the vfs-namecache, I think it is a per process one-slot directory cache. I have never studied it's performance, but I belive a good case was made for it in the 4.[34] BSD books. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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