Date: Wed, 22 Aug 2001 21:53:26 -0700 (PDT) From: Luigi Rizzo <rizzo@aciri.org> To: imp@harmony.village.org (Warner Losh) Cc: phk@critter.freebsd.dk, thierry@herbelot.com, hackers@FreeBSD.ORG, peo@sssup.it Subject: Re: clock synchronization quality via NTP ? Message-ID: <200108230453.f7N4rQi52619@iguana.aciri.org> In-Reply-To: <200108230449.f7N4n6W81268@harmony.village.org> from Warner Losh at "Aug 22, 2001 10:49: 6 pm"
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> beyond "normal HVAC" and stock xtals on the motherboard. This is > after we've done the fast interrupt hack. Without it, the other > system activity was causing enough interrupt latncy variance that we > would see more like +- 80us with outliers way off in the weeds > (+- just under 10ms!). Warner, this sounds related to a problem we are having... a student of mine is seeing sporadic but relatively large (~50-100us) variations in the period of clock interrupts (int0 calls to the assembly routine). This is in the assembler part of the interrupt service routine, so the only reason I can see for these variations is that there are some significantly large sections of code (this is a 750 MHz box) which run with interrupts disable on the CPU. Is this the case ? And if so, what is the "fast interrupt hack" that you are mentioning and how would it improve things ? thanks luigi ----------------------------------+----------------------------------------- Luigi RIZZO, luigi@iet.unipi.it . ACIRI/ICSI (on leave from Univ. di Pisa) http://www.iet.unipi.it/~luigi/ . 1947 Center St, Berkeley CA 94704 Phone: (510) 666 2927 ----------------------------------+----------------------------------------- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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