Date: Fri, 6 Nov 2015 12:42:17 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Adrian Chadd <adrian.chadd@gmail.com> Cc: Ian Lepore <ian@freebsd.org>, Hans Petter Selasky <hps@selasky.org>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, Alexander Motin <mav@freebsd.org>, FreeBSD Current <freebsd-current@freebsd.org>, Rasool Al-Saadi <ralsaadi@swin.edu.au>, Luigi Rizzo <rizzo@iet.unipi.it> Subject: Re: Timing issue with Dummynet on high kernel timer interrupt Message-ID: <20151106204217.GI65715@funkthat.com> In-Reply-To: <CAJ-Vmo=1ie6XqMCFZ1FcuD4TmD7PQGMXjODUo1eGPdaQ8wc4Tg@mail.gmail.com> References: <CA%2BhQ2%2Bhm2z0MkB-8w5xJM7%2Biz13r_ZjwmpZBnb30_D_48gaf-w@mail.gmail.com> <563C786C.1050305@selasky.org> <CA%2BhQ2%2Bj0WiGgzV119M1ZQiXP5Z7fq7deVxDPkOhvTc7hpTETKw@mail.gmail.com> <563CC186.9000807@selasky.org> <563CD533.2000909@selasky.org> <1446828229.91534.417.camel@freebsd.org> <563CDA8F.5010901@selasky.org> <563CDBF9.3090800@selasky.org> <1446830585.91534.435.camel@freebsd.org> <CAJ-Vmo=1ie6XqMCFZ1FcuD4TmD7PQGMXjODUo1eGPdaQ8wc4Tg@mail.gmail.com>
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Adrian Chadd wrote this message on Fri, Nov 06, 2015 at 11:15 -0800:
> Ideally there'd be both behaviours:
>
> * You'd specify whether a timer/sleep needs to be exact or can
> withstand some jitter (which is what linux provides); and
Isn't that what the precision argument in callout is for?
See callout_reset_sbt(9):
The sbt, pr, and flags arguments provide more control over the scheduled
time including support for higher resolution times, specifying the
precision of the scheduled time, and setting an absolute deadline instead
of a relative timeout. The callout is scheduled to execute in a time
window which begins at the time specified in sbt and extends for the
amount of time specified in pr. If sbt specifies a time in the past, the
window is adjusted to start at the current time. A non-zero value for pr
allows the callout subsystem to coalesce callouts scheduled close to each
other into fewer timer interrupts, reducing processing overhead and power
consumption. These flags may be specified to adjust the interpretation
of sbt and pr:
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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