From: Jessica Yu <jyu@cowsay.org>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: Re: [9fans] nix scheduler changes
Date: Tue, 27 May 2014 14:15:01 -0400 [thread overview]
Message-ID: <CACebkGNqEiGXqAornUx7aXTW3WARoSU-yqBTuA2gkpsHhg0C7A@mail.gmail.com> (raw)
In-Reply-To: <2f40e8ca50e83137d89718948b1b2c4b@brasstown.quanstro.net>
On Mon, May 26, 2014 at 1:14 PM, erik quanstrom <quanstro@quanstro.net> wrote:
> so, i've done a little bit more work characterizing the performance
> of the scheduler correctness changes, and i know have some understanding
> on why e.g. ping times are a bit slower.
>
> the old code essentially let processor 0 spin in runproc, other processors called
> halt. the new code uses monmwait to wait for a change on all processors.
> this has some significant impacts on performance and power use. for example,
> on my test box with 4c/8t:
>
> spin/halt monmwait spin/monmwait
> ping 8µs 14µs 8µs # ip/ping -n10 $sysname
> mk 6.26s 3.98s 3.80 # make nix kernel
> fans audible silent audible
> δpower - -24w 0 # resolution = .1A = 12w @ 120v)
>
> this seems to indicate the latency is all in runproc(), and not waiting for things
> to be ready and assuming they will be has a big performance boost.
>
> (the third column, testing spin on mach 0, plus monmwait on the others was done
> to tell if monmwait has high latency or not.)
>
> i'd really be interested to see what this does on 24c/48t machines. something
> tells me the performance impacts would be huge, and different.
>
> - erik
>
> ---
> ps. hzsched in the distribution is 10% off for HZ=100, since
> schedticks = m->ticks + HZ/10, and delaysched tests
> for > not the expected >=.
>
Nice. Excited to see how a cleaned up + simplified runproc() and the
per-Mach queues could also change things. Any reason why the ping test
w/ monmwait wasn't consistent with the performance improvement in
other areas?
next prev parent reply other threads:[~2014-05-27 18:15 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-26 17:14 erik quanstrom
2014-05-27 18:15 ` Jessica Yu [this message]
2014-05-27 19:02 ` erik quanstrom
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