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Date: Fri, 15 Jul 2011 00:46:03 +0200 (CEST) From: Jesper Juhl <jj@...osbits.net> To: linux-kernel@...r.kernel.org cc: Eric Dumazet <dada1@...mosbay.com>, Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Rusty Russell <rusty@...tcorp.com.au> Subject: Re: App blocked in futex() burns 14% CPU. On Fri, 15 Jul 2011, Jesper Juhl wrote: > So, I've recently started enabling the KDE desktop search on my box and it > runs some indexing services (naturally) to keep track of changes to files. > One of the apps it starts is a process named "virtuoso-t". This process > burns a *lot* of CPU when it's just started, but once it has caught up > with recent changes it quiets down. It doesn't quite quiet down to the > level I'd expect though. I see it constantly using 12-14% CPU time in > 'top' even when there is *nothing* going on on the machine : > > top - 00:25:09 up 2:38, 2 users, load average: 0.01, 0.04, 0.05 > Tasks: 155 total, 1 running, 153 sleeping, 0 stopped, 1 zombie > Cpu(s): 0.7%us, 0.8%sy, 3.7%ni, 94.6%id, 0.1%wa, 0.0%hi, 0.0%si, 0.0%st > Mem: 3853028k total, 2154696k used, 1698332k free, 184280k buffers > Swap: 4200992k total, 0k used, 4200992k free, 996824k cached > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > 1952 jj 39 19 362m 263m 6544 S 14 7.0 25:09.54 virtuoso-t > 1811 jj 20 0 635m 27m 17m S 2 0.7 2:49.78 knotify4 > 1928 jj 39 19 595m 26m 18m S 1 0.7 2:58.40 nepomukservices > > This box has a dual core Intel core i5-560M CPU with hyperthreading, so it > is 12-14% of a fairly capable CPU - that's rather a lot more than I'd > expect when the box is idle and there's nothing for the process to do. > > So, I tried strace'ing the process and it seems to just be blocked in > futex() most of the time (like 99%) : > > [jj@...gon ~]$ strace -p 1952 > Process 1952 attached - interrupt to quit > futex(0x3086424, FUTEX_WAIT_PRIVATE, 503, NULL > > So it's just sitting there doing nothing, which lead me to think that this > is probably not a bug in the application - if it was doing some silly > polling loop or similar I would not just see it blocked in a futex() call. > So I'm guessing something must be happening in kernel space that's burning > a lot of CPU.. I could be completely wrong of course, and if I am, please > feel free to enlighten me. > > At this point I mainly want to know if I'm the only one seeing this and if > someone has a good explanation for this, before I try to dig deeper into > it myself. > So, any ideas/explanations? > I should probably also mention that this is with a 2.6.39.3 x86_64 kernel. I don't have any idea, currently, if this is a regression compared to older kernels or if it's always been like this or what, since I've only tried running this on this kernel - it just seems wrong though.. -- Jesper Juhl <jj@...osbits.net> http://www.chaosbits.net/ Don't top-post http://www.catb.org/jargon/html/T/top-post.html Plain text mails only, please. -- 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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