From: Avi Kivity <avi@redhat.com>
To: Paul Brook <paul@codesourcery.com>
Cc: "Chris Webb" <chris@arachsys.com>,
qemu-devel@nongnu.org, 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: Mon, 05 Apr 2010 11:22:32 +0300 [thread overview]
Message-ID: <4BB99DC8.6030106@redhat.com> (raw)
In-Reply-To: <201004042253.18066.paul@codesourcery.com>
On 04/05/2010 12:53 AM, Paul Brook wrote:
>
>> 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.
>
That was 125 interrupts/sec x 10 fds ('poll' here was the per-file
callback in the kernel, not the select call). With your numbers, it's
more like 10k polls/sec which can be eliminated.
> 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.
>
I was estimating from the strace parsed output, the real number is 7.
So the kernel calls 7k callbacks/sec only to return with a timeout.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
prev parent reply other threads:[~2010-04-05 8:23 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1267068445.1726.25.camel@localhost>
[not found] ` <1267089644.12790.74.camel@laptop>
[not found] ` <1267152599.1726.76.camel@localhost>
[not found] ` <20100226090147.GH15885@elte.hu>
[not found] ` <4B879A2F.50203@redhat.com>
[not found] ` <20100226103545.GA7463@elte.hu>
[not found] ` <4B87A6BF.3090301@redhat.com>
[not found] ` <20100226111734.GE7463@elte.hu>
[not found] ` <4B8813F2.8090208@redhat.com>
[not found] ` <20100227105643.GA17425@elte.hu>
2010-02-27 13:30 ` [Qemu-devel] Re: KVM usability Jan Kiszka
[not found] ` <d9c105ea1003011312s935c3c5haa1ec80aebe14d88@mail.gmail.com>
[not found] ` <4B8C38B8.8010007@codemonkey.ws>
[not found] ` <1267498953.2460.32.camel@x200>
[not found] ` <20100302082118.GT1924@arachsys.com>
[not found] ` <428008581.20100302103400@eternallybored.org>
[not found] ` <4B938F9D.7010207@redhat.com>
2010-04-04 12:31 ` [Qemu-devel] High CPU use of -usbdevice tablet (was Re: KVM usability) Chris Webb
2010-04-04 14:25 ` Paul Brook
2010-04-04 16:58 ` Avi Kivity
2010-04-04 21:03 ` Paul Brook
2010-04-04 21:53 ` Paul Brook
2010-04-05 8:22 ` Avi Kivity [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4BB99DC8.6030106@redhat.com \
--to=avi@redhat.com \
--cc=chris@arachsys.com \
--cc=jernej's-kvm@eternallybored.org \
--cc=kvm@vger.kernel.org \
--cc=paul@codesourcery.com \
--cc=qemu-devel@nongnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).