Date: Wed, 30 May 2012 11:24:52 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Cc: Adrian Chadd <adrian@freebsd.org>, Alexander Motin <mav@freebsd.org> Subject: Re: ULE/sched issues on stable/9 - why isn't preemption occuring? Message-ID: <201205301124.52597.jhb@freebsd.org> In-Reply-To: <CAJ-VmomWV2XibSNSr5Mfh7mpKsWrX5GKsNfU9iq7TO6%2BKxxQhw@mail.gmail.com> References: <CAJ-VmomWV2XibSNSr5Mfh7mpKsWrX5GKsNfU9iq7TO6%2BKxxQhw@mail.gmail.com>
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On Tuesday, May 29, 2012 4:08:23 pm Adrian Chadd wrote: > Hi Alexander and others, > > I've been tinkering with ath(4) IO scheduling and taskqueues. In order > to get proper "in order" TX IO occuring, I've placed ath_start() into > a taskqueue so now whenever ath_start() is called, it just schedules a > taskqueue entry to run. > > However, performance is worse. :-) > > Here's a schedgraph trace. > > http://people.freebsd.org/~adrian/ath/ktr.4-ath-iperf-using-taskqueue-for- tx.ktr.gz > > I've thrown this through schedgraph.py on stable/9 and I've found some > rather annoying behaviour. It seems that the ath0 taskqueue stays in > the "runq add" state for quite a long time (1.5ms and longer) because > something else is going on on CPU #0. > > I'm very confused about what's going on. I'd like a hand trying to > figure out why the schedgraph output is the way it is. > > Thanks! As mentioned on IRC, you need to disable powerd and set machdep.idle=spin and get new traces. Right now your traces show multiple things executing on a single CPU. -- John Baldwin
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