Date: Wed, 2 Jan 2013 21:52:37 -0800 From: Kevin Oberman <kob6558@gmail.com> To: Alexander Motin <mav@freebsd.org> Cc: Davide Italiano <davide@freebsd.org>, Ian Lepore <freebsd@damnhippie.dyndns.org>, Adrian Chadd <adrian@freebsd.org>, Marius Strobl <marius@alchemy.franken.de>, FreeBSD Current <freebsd-current@freebsd.org>, freebsd-arch@freebsd.org Subject: Re: [RFC/RFT] calloutng Message-ID: <CAN6yY1vRJN8EpKpYARfkShRzmPfC4VEw33O1mfppZ%2BD%2B8iebgQ@mail.gmail.com> In-Reply-To: <50E4AF4C.2070902@FreeBSD.org> References: <50CCAB99.4040308@FreeBSD.org> <50CE5B54.3050905@FreeBSD.org> <50D03173.9080904@FreeBSD.org> <20121225232126.GA47692@alchemy.franken.de> <50DB4EFE.2020600@FreeBSD.org> <1356909223.54953.74.camel@revolution.hippie.lan> <20121231061735.GA5866@onelab2.iet.unipi.it> <50E16637.9070501@FreeBSD.org> <20130102105730.GA42542@onelab2.iet.unipi.it> <50E418EA.7030801@FreeBSD.org> <20130102122743.GA43241@onelab2.iet.unipi.it> <CAO4K=PUHAH=UNzMde0V2TwkN5vj3gw9hHj5yCQxDvdUn%2Buqv7w@mail.gmail.com> <1357135374.54953.150.camel@revolution.hippie.lan> <CAJ-Vmo=mmm5zhwHyzKeg1VEL8hSz6_LxJAaLh74ArHF3_9KWaQ@mail.gmail.com> <50E4AF4C.2070902@FreeBSD.org>
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On Wed, Jan 2, 2013 at 2:06 PM, Alexander Motin <mav@freebsd.org> wrote: > On 02.01.2013 18:08, Adrian Chadd wrote: >> >> .. I'm pretty damned sure we're going to need to enforce a "never >> earlier than X" latency. > > > Do you mean here that we should never wake up before specified time (just as > specified by the most of existing APIs), or that we should not allow sleep > shorter then some value to avoid DoS? At least on x86 nanosleep(0) doesn't > allow to block the system. Also there is already present mechanism for > specifying minimum timer programming interval in eventtimers(9) KPI. I can see serious performance issues with some hardware (wireless comes to mind) if things happen too quickly. Intuition is that it could also play hob with VMs. I believe that the proper way is to wake between T_X and T_X + D. This assumes that D is max_wake_delay, not deviation, which leaves us at the original of (T_X) =< event_time =< (T_X + D). -- R. Kevin Oberman, Network Engineer E-mail: kob6558@gmail.com
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