Date: Tue, 20 Nov 2007 20:45:05 +0300 From: Alexey Popov <lol@chistydom.ru> To: Tom Evans <tevans.uk@googlemail.com> Cc: freebsd-stable@freebsd.org, Ivan Voras <ivoras@freebsd.org> Subject: Re: 2 x quad-core system is slower that 2 x dual core on FreeBSD Message-ID: <47431D21.4050804@chistydom.ru> In-Reply-To: <1195577222.82763.20.camel@localhost> References: <4741905E.8050300@chistydom.ru> <fhs3s5$knj$1@ger.gmane.org> <47419AB3.5030008@chistydom.ru> <fhs7db$2es$1@ger.gmane.org> <4741B3DE.2000009@chistydom.ru> <fhsl0v$n85$1@ger.gmane.org> <47430AE8.7050408@chistydom.ru> <1195577222.82763.20.camel@localhost>
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Hi. Tom Evans wrote: >> After that I rebuilt with SMP GENERIC kernel and put on that server 2 >> times more requests that UP could handle. For the first time it worked >> good. Then I increased load to 2.5 times more than UP. Immediately >> Apache child count increased to MaxClients (24), most of them in RUN >> state, and %sys became greater than %user (see attach). I think after >> some threshold of load FreeBSD is paying more CPU time to the management >> of running processes than to run them. > MaxClients of 24 seems very low for a 8 cpu box, running prefork MPM. On > our quad CPU boxes, running custom apache modules, we use > MaxClients 70 > MinSpareServers 5 > MaxSpareServers 15 > StartServers 20 > Perhaps you are seeing high system load because the system is having to > maintain a lot of queued connections. Certainly, our load remains > in-between comfortable margins, except when heavily stressed. I believe 8-core FreeBSD server is able to maintain 1024 waiting TCP connections without measurable CPU load. As of this problem: increasing MaxClients leads to growing %sys part of CPU load. Generally large MaxClients value is useful when most Apache children are waiting for I/O or something else but CPU. With best regards, Alexey Popov
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