Date: Mon, 03 Nov 2008 13:15:21 +0200 From: Krassimir Slavchev <krassi@bulinfo.net> To: Julian Elischer <julian@elischer.org> Cc: freebsd-performance@freebsd.org, Sam Xia <xiazhongqi@huawei.com> Subject: Re: 1. thread switching time? (Krassimir Slavchev) Message-ID: <490EDD49.5070902@bulinfo.net> In-Reply-To: <490AB750.9040505@elischer.org> References: <000001c93b0c$6195e6b0$2f096f0a@china.huawei.com> <490AB477.2080001@bulinfo.net> <490AB750.9040505@elischer.org>
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Julian Elischer wrote: > Krassimir Slavchev wrote: > >> >> Also, I am able to set HZ=100000 but the thread switching time is still >> ~1ms. > > You must be talking about the time that a thread can run before it is > pushed out by other threads? I know I've seem many x 10,000 context > switches in some cases, i.e. look at very high interrupt rates > etc. so I guess I'm not sure what you are measuring.. > > at one time the scheduling quantum was independent of Hz. > I am not sure how true that is now.. > The scheduling quantum is independent of Hz for Hz > 1000. usr/src/sys/kern_tc.c: ... if (hz > 1000) tc_tick = (hz + 500) / 1000; else tc_tick = 1; ... I am not sure whether setting Hz > 1000 impact on performance or not, e.g using polling(4). Removing this limitation and setting kern.hz=10000 give 100usec quantum. Thanks for the point. Best Regards -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (FreeBSD) iD8DBQFJDt1JxJBWvpalMpkRAnWCAJ9z5Z7JYDC/3AdsJe+Cn7+dg6y3HwCdHPZA 6sK5dec43n41/QcbiluJoeA= =8u2E -----END PGP SIGNATURE-----
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