Date: Wed, 1 Sep 2010 12:53:04 -0500 From: Brandon Gooch <jamesbrandongooch@gmail.com> To: Alexander Motin <mav@freebsd.org> Cc: freebsd-hackers@freebsd.org, FreeBSD-Current <freebsd-current@freebsd.org> Subject: Re: One-shot-oriented event timers management Message-ID: <AANLkTikcHn-SXk7Rx6NcSQKtBh-Df-g2pzeU%2BzHor9Vy@mail.gmail.com> In-Reply-To: <4C7E2E8A.3030709@FreeBSD.org> References: <4C7A5C28.1090904@FreeBSD.org> <20100830110932.23425932@ernst.jennejohn.org> <4C7B82EA.2040104@FreeBSD.org> <20100830121148.11926306@ernst.jennejohn.org> <20100831102918.4f5404cc@ernst.jennejohn.org> <4C7CC1DE.1080907@FreeBSD.org> <4C7E2E8A.3030709@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, Sep 1, 2010 at 5:44 AM, Alexander Motin <mav@freebsd.org> wrote: > Alexander Motin wrote: >> Gary Jennejohn wrote: >>> On Mon, 30 Aug 2010 12:11:48 +0200 >>> OK, this is purely anecdotal, but I'll report it anyway. >>> >>> I was running pretty much all day with the patched kernel and things >>> seemed to be working quite well. >>> >>> Then, after about 7 hours, everything just stopped. >>> >>> I had gkrellm running and noticed that it updated only when I moved the >>> mouse. >>> >>> This behavior leads me to suspect that the timer interrupts had stopped >>> working and the mouse interrupts were causing processes to get scheduled. >>> >>> Unfortunately, I wasn't able to get a dump and had to hit reset to >>> recover. >>> >>> As I wrote above, this is only anecdotal, but I've never seen anything >>> like this before applying the patches. >> >> One-shot timers have one weak side: if for some reason timer interrupt >> getting lost -- there will be nobody to reload the timer. Such cases >> probably will require special attention. Same funny situation with >> mouse-driven scheduler happens also if LAPIC timer dies when pre-Core-iX >> CPU goes to C3 state. > > I have reproduced the problem locally. It happens more often when ticks > are not stopped on idle, like in your original case (or if explicitly > enabled by kern.eventtimer.idletick sysctl). > > I've made some changes to HPET driver, which, I hope, should fix > interrupt losses there. > > Updated patch: http://people.freebsd.org/~mav/timers_oneshot6.patch > > Patch also includes some optimizations to reduce lock contention. > > Thanks for testing. This latest patch causes an interrupt storm with the HPET timer on my system. The machine took about 8 minutes to boot and bring me to a login prompt. System interactivity (i.e. input from keyboard, output on console) was fine, but after checking the output of `systat vmstat -1`, I saw the interrupt rate on each HPET entry was over 120k! Can I provide any useful detail? Of course, test patches are always welcome :) -Brandon
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?AANLkTikcHn-SXk7Rx6NcSQKtBh-Df-g2pzeU%2BzHor9Vy>