Date: Sun, 1 Jul 2012 18:32:37 +0200 From: Davide Italiano <davide.italiano@gmail.com> To: freebsd-arch@freebsd.org Subject: Re: [RFC/RFT] callout(9): major changes Message-ID: <CACYV=-HSEe2vjcBj1eh31%2BJ4CbBcSmBPhAHK3i0B895981zM0A@mail.gmail.com> In-Reply-To: <CACYV=-GB6Q9NpK7g8dyD1ZEGO4wz%2BzjqxEJ0_di_aTpOmg%2BFXA@mail.gmail.com> References: <CACYV=-GB6Q9NpK7g8dyD1ZEGO4wz%2BzjqxEJ0_di_aTpOmg%2BFXA@mail.gmail.com>
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On Sun, Jul 1, 2012 at 3:32 PM, Davide Italiano <davide@freebsd.org> wrote: > Howdy. > As part of the Google Summer of Code project, in the last weeks, I > worked on some changes in the callout(9) subsystem, under the > mentorship of Alexander Motin (mav@). > The projects aims to adapt the callout() backend in order to exploit > better precision allowed by the recently introducted eventtimers(4/9) > subsystem. > A patch may be found here: http://people.freebsd.org/~davide/callout_patch.diff > If you want to try the code may be found in FreeBSD svn projects/ > repository: http://svnweb.freebsd.org/base/projects/calloutng/ > At the time of writing, the code cannot be considered ready for hit > the tree, some work is still missing, but some goals have been > reached. In particular: > > - The callout(9) backend was completely switched from a tick-based > approach to a tickless one. > - The code has been integrated with the eventtimers > - An experimental new KPI has been introduced so that timeouts for > callout_* may be specified also in terms of bintime other than ticks, > as previously allowed > - Support for execution of callouts from hw interrupt context has been > introduced > - In order to prove effectiveness of the approach, some consumers (in > particular sleep/pool/select) have been ported to the new KPI, and the > changes have been microbenchmarked > - Some experiments of event aggregation have been done, as well as the > definition of new KPI in which consumers may specify granularity at > which events may be aggregated. > > For my benchmarks I used the same program luigi@ has recently used, > even though results are a bit different > (http://lists.freebsd.org/pipermail/freebsd-arch/2012-February/012413.html). > Just a bit of results: > Sequential usleep(): > This graph shows on the x-axes the timeout se and on y-axes the real > sleep time (in the range [1;1000]). Timeout is increased sequentially > by one unit every iteration. Green line represents the "ideal" case, > Red line represents results after the changes made. > http://people.freebsd.org/~davide/sequential_new.png > Random sleep(): > same as before, but in this case I plotted the delta among the > expected sleep time and the actual sleep time. > http://people.freebsd.org/~davide/delta_random.png > Random select(): > http://people.freebsd.org/~davide/delta_random.png Sorry, this is the correct link for random select() results: http://people.freebsd.org/~davide/random_new.png > > I'd like to have some feedback/comments on the implementative choices > I've done, as well as on the new defined KPI or future directions. > If you've any question, feel free to ask. > > Davide Davide
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