From: Gleb Natapov <gleb@redhat.com>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Mohamad Gebai <mohamad.gebai@polymtl.ca>,
kvm@vger.kernel.org, linux-perf-users@vger.kernel.org
Subject: Re: Tracing kvm: kvm_entry and kvm_exit
Date: Tue, 26 Feb 2013 18:32:54 +0200 [thread overview]
Message-ID: <20130226163254.GA26996@redhat.com> (raw)
In-Reply-To: <20130225101804.GC2790@stefanha-thinkpad.redhat.com>
On Mon, Feb 25, 2013 at 11:18:04AM +0100, Stefan Hajnoczi wrote:
> On Fri, Feb 22, 2013 at 11:34:27AM -0500, Mohamad Gebai wrote:
> > I am tracing kvm using perf and I am analyzing the sequences of kvm_entry and
> > kvm_exit tracepoints.
> > I noticed that during the boot process of a VM, there are a lot more (2 to 3 as
> > many times) kvm_entry event than there are kvm_exit. I tried looking around but
> > didn't find anything that explains this. Is this missing instrumentation? Or
> > what other path does kvm take that doesn't generate a kvm_exit event?
>
> Gleb Natapov noticed something similar when playing with the perf script
> I posted here:
>
> http://permalink.gmane.org/gmane.comp.emulators.kvm.devel/104181
>
> Perhaps there is a code path that is missing trace_kvm_exit().
>
During guest boot there is such path. If instruction is emulated entry
is reported but exit is not. What we saw with perf was different though,
It was during normal run, not boot, so emulation cannot explain it.
> We didn't investigate why it happens but the unexplained kvm_entry
> events only appeared at the beginning of the trace, so the theory was
> that events are not activated atomically by perf(1).
>
> CCing perf mailing list.
>
> It would be interesting if someone knows the answer.
>
> Stefan
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
Gleb.
next prev parent reply other threads:[~2013-02-26 16:33 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1361550867.51279e13338a7@www.imp.polymtl.ca>
2013-02-25 10:18 ` Tracing kvm: kvm_entry and kvm_exit Stefan Hajnoczi
2013-02-26 16:24 ` Mohamad Gebai
2013-02-26 16:32 ` Gleb Natapov [this message]
2013-02-27 16:39 ` David Ahern
2013-02-28 4:49 ` David Ahern
2013-02-28 8:44 ` Stefan Hajnoczi
2013-03-04 5:36 ` Mohamad Gebai
2013-03-04 5:40 ` David Ahern
2013-03-04 6:15 ` Mohamad Gebai
2013-03-05 17:23 ` David Ahern
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=20130226163254.GA26996@redhat.com \
--to=gleb@redhat.com \
--cc=kvm@vger.kernel.org \
--cc=linux-perf-users@vger.kernel.org \
--cc=mohamad.gebai@polymtl.ca \
--cc=stefanha@gmail.com \
/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).