Date: Mon, 22 Sep 2003 14:22:02 -0700 From: Luigi Rizzo <rizzo@icir.org> To: "akanwar@digitarchy.com" <akanwar@digitarchy.com> Cc: freebsd-hackers@freebsd.org Subject: Re: HZ = 1000 slows down application Message-ID: <20030922142202.A46421@xorpc.icir.org> In-Reply-To: <63340-220039122184340901@M2W048.mail2web.com>; from akanwar@digitarchy.com on Mon, Sep 22, 2003 at 02:43:40PM -0400 References: <63340-220039122184340901@M2W048.mail2web.com>
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On Mon, Sep 22, 2003 at 02:43:40PM -0400, akanwar@digitarchy.com wrote: ... > But now I noticed that my application is occassionally doing slower > iterations. Average iteration time used to be 0.2 ms without polling > enabled. With the device polling changes, the average time is still around > the same, but once every few minutes the application sees iterations that > are 3.3 seconds (*seconds*, not a typo) long. most likely your application makes some assumptions on the duration of a clock tick and then it gets confused when, say, a select returns quicker, or some time difference becomes negative, etc. etc. because of the finer granularity. very common type of bug. cheers luigi > This seems to happen as soon as I use the kernel with HZ=1000. Enabling or > disabling device polling does not seem to make any difference to this > behavior. I am trying to understand why there seem to be a few really long > iterations. Could it happen that the application does not get any CPU for > that long? Seems very counter intuitive that higher HZ should cause this. > > Could anyone shed any light on what is happening ? > > Thanks, > -ansh > > -------------------------------------------------------------------- > mail2web - Check your email from the web at > http://mail2web.com/ . > > > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org" >
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