Date: Thu, 28 Aug 2008 09:38:31 +1000 From: Andrew Reilly <andrew-freebsd@areilly.bpc-users.org> To: Jeff Roberson <jroberson@jroberson.net> Cc: freebsd-multimedia@freebsd.org, freebsd-arch@freebsd.org Subject: Re: SCHED_ULE problem: slow single processor, realtime prio vs network stack Message-ID: <20080827233831.GA16705@duncan.reilly.home> In-Reply-To: <20080820214627.C30593@desktop> References: <20080819025019.GA27997@duncan.reilly.home> <20080818215813.H952@desktop> <20080819134005.GA85664@duncan.reilly.home> <20080820214627.C30593@desktop>
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On Wed, Aug 20, 2008 at 09:47:01PM -1000, Jeff Roberson wrote: > On Tue, 19 Aug 2008, Andrew Reilly wrote: > >I haven't tried nice -20 because I don't want the priority to > >drift or change, which is something that I thought the normal > >levels did. I'll give it a go though, and report back. > > With such a low cpu utilization I wouldn't expect it's the scheduling > algorithm. It may be a difference in preemption settings. Is preemption > enabled in both kernels? I've just done a set of tests with setprio(... -20) vs rtprio(...10), and with SCHED_ULE vs SCHED_4BSD. The results are essentially as I reported before except that regular prio -20 seems to be just as reliable as rtprio 10 under 4BSD and just as unhelpful under _ULE. To summarise: SCHED_ULE: rtprio 10: network activity causes audio underruns SCHED_ULE: setprio -20: network activity causes audio underruns SCHED_4BSD: rtprio 10: no audio underruns SCHED_4BSD: setprio -20: no audio underruns For what it's worth, my audio buffering setup has a fragment size of 0.7ms, but several buffers. How is device driver activity prioritized? Does the scheduler in use effect how device interrupts are handled, as well as user-land tasks? I have kernels built with both schedulers sitting arround on this machine now, so it's easy to switch back and forth if there are some specific tests that I could do or other information that I could provide. Cheers, Andrew
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