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Date:      Fri, 6 Nov 2015 11:15:49 -0800
From:      Adrian Chadd <adrian.chadd@gmail.com>
To:        Ian Lepore <ian@freebsd.org>
Cc:        Hans Petter Selasky <hps@selasky.org>, Luigi Rizzo <rizzo@iet.unipi.it>,  Rasool Al-Saadi <ralsaadi@swin.edu.au>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>,  Alexander Motin <mav@freebsd.org>, FreeBSD Current <freebsd-current@freebsd.org>
Subject:   Re: Timing issue with Dummynet on high kernel timer interrupt
Message-ID:  <CAJ-Vmo=1ie6XqMCFZ1FcuD4TmD7PQGMXjODUo1eGPdaQ8wc4Tg@mail.gmail.com>
In-Reply-To: <1446830585.91534.435.camel@freebsd.org>
References:  <6545444AE21C2749939E637E56594CEA3C0DCCC4@gsp-ex02.ds.swin.edu.au> <5638B7B5.3030802@selasky.org> <6545444AE21C2749939E637E56594CEA3C0DE7FF@gsp-ex02.ds.swin.edu.au> <563B2703.5080402@selasky.org> <6545444AE21C2749939E637E56594CEA3C0E0BD9@gsp-ex02.ds.swin.edu.au> <563C6864.2090907@selasky.org> <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>

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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
* You can communicate to the kernel its aggressiveness for coalescing wakeups.

Teaching powerd to flip on/off a sysctl for this isn't that tricky. I
remember seeing someone else in #bsdmips having issues figuring out
sleep-in-kernel durations and it being exactly this stuff (and it
being you, Ian, that figured it out) - so I'd like to at least fix it
in -head this time around!

Also - I thought the other issue was that precise callouts (versus the
default for callouts now which is "fuzzy" unless you specify
precision) were still jittering. Is that the case?

Thanks,

-adrian



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