Date: Wed, 23 Feb 2005 14:15:40 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Chris <chrcoluk@gmail.com> Cc: cpghost@cordula.ws Subject: Re: HZ=1000 on slow CPUs considered harmful? Message-ID: <Pine.NEB.3.96L.1050223141425.68237N-100000@fledge.watson.org> In-Reply-To: <3aaaa3a05022306033a4f3d96@mail.gmail.com>
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On Wed, 23 Feb 2005, Chris wrote: > I have noticed issues with HZ=1000 on a celeron 2ghz and a AMD64 3.2ghz, > both caused problems with glftpd app and I had to recompile kernel back > to default HZ=100 to fix, I have also noticed HZ=1000 add latency on my > celeron box. FYI, the recent tcp_subr.c changes I merged may help with performance at higher HZ levels. Basically, the tcp_isn_tick() function, which stirs up the initial sequence number pot at intervals, was running ten times as often as it needed to, as it ran each tick rather than at a fixed rate/second. Robert N M Watson > > Chris > > > On Tue, 22 Feb 2005 14:00:09 -0800, Kevin Oberman <oberman@es.net> wrote: > > > Date: Tue, 22 Feb 2005 22:48:21 +0100 > > > From: cpghost@cordula.ws > > > > > > On Tue, Feb 22, 2005 at 07:56:03PM +0000, Robert Watson wrote: > > > > In 6-CURRENT, HZ is 1000 for amd64, i386, and ia64, but 100 for other > > > > platforms (i.e., ppc, arm, and alpha). I'm not opposed to merging the HZ > > > > change to RELENG_5 at some point, but given that occasional nits, such as > > > > the TCP nit, are turning up, I think it's worth waiting until after 5.4. > > > > > > Wouldn't that be a problem for slow CPUs like VIA C3 (EPIA) or GEODE > > > (Soekris)? For fast CPUs, it's not that much overhead, but for slow > > > CPUs? > > > > > > Can HZ remain user-configurable? > > > > > > > Robert N M Watson > > > > > > Thanks, > > > -cpghost. > > > > > > -- > > > Cordula's Web. http://www.cordula.ws/ > > > > > > > As far as I know, no one is talking about removing the knob. I believe > > the issue is the default value changing from 100 to 1000. There are many > > boxes that would not be very happy with 1000. I'm sure that there are > > many 75 MHz Pentiums and 66 MHz 486s still running FreeBSD and even running > > V5. > > -- > > R. Kevin Oberman, Network Engineer > > Energy Sciences Network (ESnet) > > Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) > > E-mail: oberman@es.net Phone: +1 510 486-8634 > > _______________________________________________ > > freebsd-stable@freebsd.org mailing list > > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org" > > >
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