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Date: Mon, 20 Dec 2010 16:11:24 +0100 From: Jiri Olsa <jolsa@...hat.com> To: Dave Jones <davej@...hat.com>, linux-kernel@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>, Alan Cox <alan@...rguk.ukuu.org.uk>, Arnd Bergmann <arnd@...db.de> Subject: Re: flush_to_ldisc executing 2500 times a second ? hi, sorry for late reply, I just got back from vacation.. is this still an issue? thanks, jirka On Tue, Nov 30, 2010 at 11:07:09PM -0500, Dave Jones wrote: > While poking at an unrelated bug, I came up with a perf > command line that showed something curious. > > perf record -a -e workqueue:workqueue_execute_start sleep 1 > perf trace > > shows flush_to_ldisc being executed ~2500 times. > (http://codemonkey.org.uk/junk/flush_to_ldisc.txt) > > Steve Rostedt gave me a tip about trace-cmd to get a backtrace, > > trace-cmd record -e workqueue_queue_work -O stacktrace sleep 1 > > which yields thousands of .. > > sleep-17431 [000] 35746.452637: workqueue_queue_work: work struct=0xffff880113f2a2a0 function=flush_to_ldisc workqueue=0xffff88013f80cb68 req_cpu=0 cpu=0 > sleep-17431 [000] 35746.452638: kernel_stack: <stack trace> > => __queue_work (ffffffff81068c25) > => delayed_work_timer_fn (ffffffff81068cc8) > => run_timer_softirq (ffffffff8105e651) > => __do_softirq (ffffffff810571af) > => call_softirq (ffffffff8100bbdc) > => do_softirq (ffffffff8100d358) > => irq_exit (ffffffff81057366) > => smp_apic_timer_interrupt (ffffffff81482b9e) > > Which doesn't really tell me much. > > > At the time of the profiling, there's nothing being output on any tty's > (and the profiling tools are also silent during the actual profiling) so > I'm curious as to what's causing the flushing to be necessary. > > Anyone have any ideas what's going on here ? or something further > I could dig into ? > > This is with 2.6.37-rc4. > > The only other machine I have to test on right now is running 2.6.34, which > doesn't exhibit this behaviour. I'll try to narrow it down further tomorrow. > > Dave > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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