Date: Wed, 20 Sep 2006 08:24:08 -0500 From: Eric Anderson <anderson@centtech.com> To: freebsd-hackers@freebsd.org Subject: Re: numbers don't lie ... Message-ID: <451140F8.9030500@centtech.com> In-Reply-To: <200609201250.k8KCo8sm048910@lurza.secnetix.de> References: <200609201250.k8KCo8sm048910@lurza.secnetix.de>
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On 09/20/06 07:50, Oliver Fromme wrote: > Dmitry Morozovsky wrote: > > Oliver Fromme wrote: > > > Because buildworld is I/O-bound on systems with sufficiently > > > fast processors. > > > > > > Try putting the contents of /usr/src into a RAM disk and > > > repeat the benchmark. The numbers might look a little > > > different then. Of course, you should have sufficient RAM > > > in the machines -- If they're going to swap to the disks, > > > your benchmark won't be happy. > > > > > > I think putting /usr/obj onto a RAM disk is _not_ necessary > > > because of soft-updates, so the processes shouldn't block > > > on writes. > > > > My experiments show that if you have enough memory to host radmdrive for > > /usr/src you'd better leave it for caching - there were no statistically > > meaningful performance difference, at least on machines with 1G+ RAM. > > That might only be true if you have enough RAM to keep > _all_ buildworld files (src, obj, toolchain) in the cache > _and_ you pre-read all of /usr/src before actually starting > the buildworld, so it is in the cache. If you don't have > that much RAM, but enough to store /usr/src, then using > a RAM disk for it is a win. > > Reading /usr/src from a physical disk certainly requires > quite some I/O that takes more than zero time. But, in order to populate the ram disk, you must read /usr/src also from something, and that also takes time, which you should include in the full scope. Eric -- ------------------------------------------------------------------------ Eric Anderson Sr. Systems Administrator Centaur Technology Anything that works is better than anything that doesn't. ------------------------------------------------------------------------
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