Date: Fri, 29 Oct 2010 23:44:13 +0300 From: Alexander Motin <mav@FreeBSD.org> To: Takanori Watanabe <takawata@init-main.com> Cc: acpi@freebsd.org, current@freebsd.org, hselasky@c2i.net Subject: Re: Event based scheduling and USB. Message-ID: <4CCB321D.1020502@FreeBSD.org> In-Reply-To: <4CC732C7.50409@FreeBSD.org> References: <201010261904.o9QJ4iwq089834@sana.init-main.com> <4CC732C7.50409@FreeBSD.org>
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Alexander Motin wrote: > Takanori Watanabe wrote: >> I updated my FreeBSD tree on laptop, to the current >> as of 18 Oct.2010, it works fine with CPU C3 state enabled, >> >> I think this is your achievement of event time scheduler, >> thanks! >> >> But when USB driver is enabled, the load average is considerablly >> high (0.6 to 1.0) if sysctl oid kern.eventtimer.periodic is set to 0. >> Then kern.eventtimer.periodic is set to 1, the load average goes >> to 0 quickly as before, but almost never transit to C3. >> >> Is this behavior expected, or something wrong? >> I noticed one of usb host controller device shares HPET irq. >> When I implement interrupt filter in uhci driver, the load average >> goes to 0 as before. >> >> ==== >> % vmstat -i >> interrupt total rate >> irq1: atkbd0 398 2 >> irq9: acpi0 408 2 >> irq12: psm0 3 0 >> irq19: ehci1 37 0 >> irq20: hpet0 uhci0 35970 230 >> irq22: ehci0 2 0 >> irq256: em0 4 0 >> irq257: ahci0 1692 10 >> Total 38514 246 >> === > > I haven't noticed that issue and it is surely not expected for me. I > will try to reproduce it. I've easily reproduced the problem. Scheduler tracing shows that problem is the result of aliasing between "swi4: clock" thread on one CPU (measuring load average) and "irq21: hpet0 uhci1" thread on another. Those two events are aliased by definition due to shared interrupt source. Not sure what to do with it. Either we should change algorithm of load average calculation or exclude timer's interrupt threads from load average accounting. Adding interrupt filter for USB also reasonably helps, but it is only a partial solution for this specific sharing case. -- Alexander Motin
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