Re: Netperf UDP_STREAM regression due to not sending IPIs inttwu_queue()

From: Mel Gorman
Date: Tue Oct 02 2012 - 09:14:21 EST


On Tue, Oct 02, 2012 at 11:31:22AM +0200, Mike Galbraith wrote:
> On Tue, 2012-10-02 at 09:45 +0100, Mel Gorman wrote:
> > On Tue, Oct 02, 2012 at 09:49:36AM +0200, Mike Galbraith wrote:
>
> > > Hm, 518cd623 fixed up the troubles I saw. How exactly are you running
> > > this?
> > >
> >
> > You saw problems with TCP_RR where as this is UDP_STREAM.
>
> Yeah, but I wanted to stare at UDP_STREAM as you run it to see if it
> would tell me anything about why those numbers happen.
>
> > I'm running this through MMTests with a version of the
> > configs/config-global-dhp__network-performance file that only runs
> > netperf-udp. Ultimately it runs netperf for a size something like
> > this
> >
> > SIZE=64
> > taskset -c 0 netserver
> > taskset -c 1 netperf -t UDP_STREAM -i 50,6 -I 99,1 -l 20 -H 127.0.0.1 -- -P 15895 -s 32768 -S 32768 -m $SIZE -M $SIZE
>

lock_stat points at the runqueue lock which makes sense as without the
IPI the rq->lock has to be taken

3.3.0-vanilla
class name con-bounces contentions waittime-min waittime-max waittime-total acq-bounces acquisitions holdtime-min holdtime-max holdtime-total
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
&rq->lock: 37062 37063 0.08 10.43 11037.66 410701252 1029063029 0.00 14.35 234556106.12
---------
&rq->lock 14064 [<ffffffff81420a76>] __schedule+0xc6/0x710
&rq->lock 33 [<ffffffff8107791d>] idle_balance+0x13d/0x190
&rq->lock 11810 [<ffffffff8106cac7>] ttwu_queue+0x47/0xf0
&rq->lock 283 [<ffffffff81067f86>] task_rq_lock+0x56/0xa0
---------
&rq->lock 22305 [<ffffffff8106cac7>] ttwu_queue+0x47/0xf0
&rq->lock 11260 [<ffffffff81420a76>] __schedule+0xc6/0x710
&rq->lock 158 [<ffffffff8107791d>] idle_balance+0x13d/0x190
&rq->lock 8 [<ffffffff810772a6>] load_balance+0x356/0x500

3.3.0-revert
&rq->lock: 10831 10833 0.09 10.47 4448.19 87877 768253556 0.00 16.00 140103672.33
---------
&rq->lock 685 [<ffffffff810771d8>] load_balance+0x348/0x500
&rq->lock 8688 [<ffffffff8106d045>] try_to_wake_up+0x215/0x2e0
&rq->lock 1010 [<ffffffff814209b6>] __schedule+0xc6/0x710
&rq->lock 228 [<ffffffff81067f86>] task_rq_lock+0x56/0xa0
---------
&rq->lock 3317 [<ffffffff814209b6>] __schedule+0xc6/0x710
&rq->lock 789 [<ffffffff810771d8>] load_balance+0x348/0x500
&rq->lock 363 [<ffffffff810770a4>] load_balance+0x214/0x500
&rq->lock 2 [<ffffffff810771e6>] load_balance+0x356/0x500

Note the difference in acq-bounces. I had to stop at this point and move
back to some CMA breakage I introduced.

--
Mel Gorman
SUSE Labs
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