From: Paul Brook <paul@codesourcery.com> To: qemu-devel@nongnu.org Cc: "Avi Kivity" <avi@redhat.com>, "Chris Webb" <chris@arachsys.com>, kvm@vger.kernel.org, "Jernej Simončič" <jernej's-kvm@eternallybored.org> Subject: Re: [Qemu-devel] High CPU use of -usbdevice tablet (was Re: KVM usability) Date: Sun, 4 Apr 2010 22:53:17 +0100 [thread overview] Message-ID: <201004042253.18066.paul@codesourcery.com> (raw) In-Reply-To: <4BB8C51A.6070908@redhat.com> > > My guess is that the overhead you're seeing is entirely from the USB host > > adapter having to wake up and check the transport descriptor lists. This > > will only result in the guest being woken if a device actually responds > > (as mentioned above it should not). > > A quick profile on the host side doesn't show this. Instead, I see a > lot of select() overhead. This actually confirms my hypothesis. After fixing the UHCI bug the guest is completely idle, but the host still needs to wake up at 1ms intervals to do UHCI emulation. I can believe that the most visible part of this is the select() syscall. > Surprising as there are ~10 descriptors being > polled, so ~1200 polls per second. Maybe epoll will help here. I'm not sure where you get 1200 from. select will be called once per host wakeup. i.e. if the USB controller is enabled then 1k times per second due to the frame tick. Are you sure there are actually 10 descriptors being polled? Remember that the nfds argument is the value of the largest fd in the set (+1), not the number of descriptors in the set. Paul
WARNING: multiple messages have this Message-ID (diff)
From: Paul Brook <paul@codesourcery.com> To: qemu-devel@nongnu.org Cc: "Chris Webb" <chris@arachsys.com>, Jernej@gnu.org, "Avi Kivity" <avi@redhat.com>, kvm@vger.kernel.org, Simončič <jernej's-kvm@eternallybored.org> Subject: Re: [Qemu-devel] High CPU use of -usbdevice tablet (was Re: KVM usability) Date: Sun, 4 Apr 2010 22:53:17 +0100 [thread overview] Message-ID: <201004042253.18066.paul@codesourcery.com> (raw) In-Reply-To: <4BB8C51A.6070908@redhat.com> > > My guess is that the overhead you're seeing is entirely from the USB host > > adapter having to wake up and check the transport descriptor lists. This > > will only result in the guest being woken if a device actually responds > > (as mentioned above it should not). > > A quick profile on the host side doesn't show this. Instead, I see a > lot of select() overhead. This actually confirms my hypothesis. After fixing the UHCI bug the guest is completely idle, but the host still needs to wake up at 1ms intervals to do UHCI emulation. I can believe that the most visible part of this is the select() syscall. > Surprising as there are ~10 descriptors being > polled, so ~1200 polls per second. Maybe epoll will help here. I'm not sure where you get 1200 from. select will be called once per host wakeup. i.e. if the USB controller is enabled then 1k times per second due to the frame tick. Are you sure there are actually 10 descriptors being polled? Remember that the nfds argument is the value of the largest fd in the set (+1), not the number of descriptors in the set. Paul
next prev parent reply other threads:[~2010-04-04 21:53 UTC|newest] Thread overview: 109+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <1267068445.1726.25.camel@localhost> [not found] ` <1267089644.12790.74.camel@laptop> 2010-02-26 2:49 ` Enhance perf to support KVM Zhang, Yanmin 2010-02-26 9:01 ` Ingo Molnar 2010-02-26 9:53 ` Avi Kivity 2010-02-26 10:35 ` Ingo Molnar 2010-02-26 10:47 ` Avi Kivity 2010-02-26 11:17 ` Ingo Molnar 2010-02-26 11:44 ` Avi Kivity 2010-02-26 12:46 ` Ingo Molnar 2010-02-26 12:54 ` Avi Kivity 2010-02-26 13:16 ` Ingo Molnar 2010-02-26 13:57 ` Jes Sorensen 2010-02-26 14:04 ` Avi Kivity 2010-02-26 14:23 ` Ingo Molnar 2010-02-26 15:06 ` Avi Kivity 2010-03-02 16:46 ` Paolo Bonzini 2010-03-02 17:12 ` Arnaldo Carvalho de Melo 2010-03-02 17:20 ` Paolo Bonzini 2010-03-02 17:24 ` Ingo Molnar 2010-03-02 17:17 ` Ingo Molnar 2010-03-07 14:17 ` Avi Kivity 2010-02-26 18:33 ` Avi Kivity 2010-02-27 10:56 ` KVM usability Ingo Molnar 2010-02-27 13:30 ` Jan Kiszka 2010-02-27 13:30 ` [Qemu-devel] " Jan Kiszka 2010-02-27 14:48 ` Ian Kirk 2010-02-27 15:32 ` Zachary Amsden 2010-02-27 17:25 ` Ingo Molnar 2010-03-01 15:33 ` Anthony Liguori 2010-03-01 16:48 ` Zachary Amsden 2010-03-01 17:41 ` Arnaldo Carvalho de Melo 2010-03-01 18:29 ` Zachary Amsden 2010-03-01 20:56 ` Ingo Molnar 2010-03-01 21:45 ` Anthony Liguori 2010-03-01 22:06 ` Zachary Amsden 2010-03-02 0:33 ` Ingo Molnar 2010-03-02 0:30 ` Ingo Molnar 2010-03-02 2:34 ` Anthony Liguori 2010-03-02 8:39 ` Chris Webb 2010-03-07 18:42 ` Avi Kivity 2010-03-02 10:30 ` Ingo Molnar 2010-03-07 9:35 ` Avi Kivity 2010-03-07 9:56 ` Pekka Enberg 2010-03-07 10:11 ` Avi Kivity 2010-03-07 18:42 ` Ingo Molnar 2010-03-07 15:14 ` Luca Barbieri 2010-03-07 18:16 ` Avi Kivity 2010-03-07 18:01 ` Arnaldo Carvalho de Melo 2010-03-07 18:15 ` Avi Kivity 2010-03-07 18:53 ` Arnaldo Carvalho de Melo 2010-03-07 19:05 ` Avi Kivity 2010-03-07 18:25 ` Avi Kivity 2010-03-01 9:25 ` Ingo Molnar 2010-03-01 15:36 ` Anthony Liguori 2010-03-01 15:14 ` Anthony Liguori 2010-03-01 15:42 ` Daniel P. Berrange 2010-03-02 1:12 ` Dustin Kirkland 2010-03-02 10:11 ` Peter Zijlstra 2010-03-02 13:37 ` Nikolai K. Bochev 2010-03-02 14:22 ` Gerd Hoffmann 2010-03-02 14:29 ` Ingo Molnar 2010-03-07 9:22 ` Avi Kivity 2010-03-02 14:37 ` Daniel P. Berrange 2010-03-02 14:52 ` Gerd Hoffmann 2010-03-02 14:56 ` Daniel P. Berrange 2010-03-02 15:13 ` Gerd Hoffmann 2010-03-04 20:00 ` Lucas Meneghel Rodrigues 2010-03-04 20:13 ` Zachary Amsden 2010-03-04 20:34 ` Anthony Liguori 2010-03-04 22:23 ` H. Peter Anvin 2010-03-05 7:44 ` Markus Armbruster 2010-03-07 11:25 ` Avi Kivity 2010-03-01 21:12 ` Dustin Kirkland 2010-03-01 21:59 ` Anthony Liguori 2010-03-02 2:34 ` Alexander Graf 2010-03-02 2:36 ` Anthony Liguori 2010-03-09 13:32 ` Avi Kivity 2010-03-09 14:32 ` Dustin Kirkland 2010-03-09 14:38 ` Alexander Graf 2010-03-09 14:50 ` Anthony Liguori 2010-03-09 14:52 ` Avi Kivity 2010-03-09 14:57 ` Anthony Liguori 2010-03-09 17:11 ` Avi Kivity 2010-03-09 17:27 ` Anthony Liguori 2010-03-09 17:30 ` Avi Kivity 2010-03-09 14:49 ` Anthony Liguori 2010-03-09 14:54 ` Avi Kivity 2010-03-02 3:02 ` Dustin Kirkland 2010-03-02 8:21 ` Chris Webb 2010-03-02 14:54 ` Dustin Kirkland [not found] ` <428008581.20100302103400@eternallybored.org> 2010-03-07 11:35 ` Avi Kivity 2010-04-04 12:31 ` High CPU use of -usbdevice tablet (was Re: KVM usability) Chris Webb 2010-04-04 12:31 ` [Qemu-devel] " Chris Webb 2010-04-04 14:25 ` Paul Brook 2010-04-04 14:25 ` Paul Brook 2010-04-04 16:58 ` Avi Kivity 2010-04-04 16:58 ` Avi Kivity 2010-04-04 21:03 ` Paul Brook 2010-04-04 21:03 ` Paul Brook 2010-04-04 21:53 ` Paul Brook [this message] 2010-04-04 21:53 ` Paul Brook 2010-04-05 8:22 ` Avi Kivity 2010-04-05 8:22 ` Avi Kivity 2010-03-03 2:57 ` KVM usability Ross Boylan 2010-03-03 8:55 ` Daniel P. Berrange 2010-03-03 15:42 ` Ross Boylan 2010-03-07 14:29 ` Avi Kivity 2010-02-26 11:48 ` Enhance perf to support KVM Peter Zijlstra 2010-02-26 11:53 ` Avi Kivity 2010-02-26 20:17 ` Anthony Liguori
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