Date: Tue, 29 May 2012 13:08:23 -0700 From: Adrian Chadd <adrian@freebsd.org> To: Alexander Motin <mav@freebsd.org>, freebsd-hackers@freebsd.org Subject: ULE/sched issues on stable/9 - why isn't preemption occuring? Message-ID: <CAJ-VmomWV2XibSNSr5Mfh7mpKsWrX5GKsNfU9iq7TO6%2BKxxQhw@mail.gmail.com>
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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! Adrian
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