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From: Yanmin Zhang <yanmin_zhang@linux.intel.com>
To: Stephane Eranian <eranian@google.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>,
	linux-kernel@vger.kernel.org, peterz@infradead.org,
	mingo@elte.hu, robert.richter@amd.com,
	Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH] perf: fix broken perf inject -b
Date: Fri, 03 Feb 2012 11:30:29 +0800	[thread overview]
Message-ID: <1328239829.14415.258.camel@ymzhang> (raw)
In-Reply-To: <CABPqkBRe76z9KwdqOoaT6JmMFFmadG3Ltck-8y+fY8qUCcECQA@mail.gmail.com>

On Thu, 2012-02-02 at 12:22 +0100, Stephane Eranian wrote:
> On Tue, Jan 31, 2012 at 6:58 AM, Yanmin Zhang
> <yanmin_zhang@linux.intel.com> wrote:
> > On Mon, 2012-01-30 at 18:36 -0200, Arnaldo Carvalho de Melo wrote:
> >> Em Mon, Jan 30, 2012 at 09:09:17PM +0100, Stephane Eranian escreveu:
> >> > On Mon, Jan 30, 2012 at 9:04 PM, Arnaldo Carvalho de Melo
> >> > <acme@redhat.com> wrote:
> >> > > Em Mon, Jan 30, 2012 at 08:53:26PM +0100, Stephane Eranian escreveu:
> >> > >> On Mon, Jan 30, 2012 at 8:00 PM, Arnaldo Carvalho de Melo
> >> > >> <acme@redhat.com> wrote:
> >> > >> > > >>> @@ -173,6 +178,7 @@ static int perf_event__inject_buildid(struct perf_tool *tool,
> >> > >> > > >>>               goto repipe;
> >> > >> > > >>>       }
> >> > >> > > >>> +     machine->pid = event->ip.pid;
> >> > >> >
> >> > >> > > I noticed that this statement conflicts with perf buildid-list (which
> >> > >> > > I am also fixing for pipe mode).
> >>
> >> > >> > > I don't quite understand why, though.
> >>
> >> > >> > Have you reached any conclusion about this problem? I haven't looked at
> >> > >> > it in detail, could you please elaborate more?
> >>
> >> > >> I ended up removing it. But I am not sure this is correct.
> >> > >> Is the pid used in any way when processing buildids?
> >> > >
> >> > > I can't think of any.
> >> > >
> >> > > The same DSO could conceivably be present in the virtual machine, the
> >> > > host, and in the workstation used for perf report.  We just use the
> >> > > build-id in the perf.data file to find the right symtab.
> >>
> >> > Right, so I don't know why it's there...
> >>
> >> This comes from a1645ce1:
> >>
> >> commit a1645ce12adb6c9cc9e19d7695466204e3f017fe
> >> Author: Zhang, Yanmin <yanmin_zhang@linux.intel.com>
> >> Date:   Mon Apr 19 13:32:50 2010 +0800
> >>
> >>     perf: 'perf kvm' tool for monitoring guest performance from host
> >>
> >>     Here is the patch of userspace perf tool.
> >>
> >>     Signed-off-by: Zhang Yanmin <yanmin_zhang@linux.intel.com>
> >>     Signed-off-by: Avi Kivity <avi@redhat.com>
> >>
> >>
> >>
> >> Zhang, what was the thinking about that pid in the buildid event?
> > I didn't work on it for a long time because of some special reasons.
> > I check it quickly and below are some explanation.
> >
> > machine->pid is to support KVM multiple guest os kernels.
> > 1) The guest os kernels might be different version of kernels from host's;
> > 2) The guest os might be Windows.
> >
> I understand that.
> 
> > At host side, every guest os is a process of host although it's multi-threaded.
> Yes.
> > machine->pid is to save its pid. The pid of host itself is HOST_KERNEL_ID.
> >
> What do you mean by the 'pid of the host'? You always capture samples on the
> host on behalf of a host task. I see PID:-1 to simulate mmap of the kernel in
> the perf.data file. Is that what you are referring to?
Yes.

> 
> > In guest os, there are many processes. host os doesn't know them. So currently or
> 
> Yes.
> 
> > when I enhanced perf to support KVM, perf filters out guest os user space
> > detailed event samples while still keeping guest os user space simple counters.
> >
> That is not clear to me. Are you saying, you have no visibility into
> the guest OS
> user space processes, samples captured at that level are attributed to
> guest kernel?
> Or are you simply dropping them?
It depends specific perf subcommand.
1) With per top, besides the specific function symbol statistics, it also shows
the total percent of host_kernel/host_user/guest_kernel/guest_user.
With the function symbol statistics, we drop guest user space data.
With the total percent, we keep them into the calculation of guest user.
static void perf_top__mmap_read_idx(struct perf_top *top, int idx)
{
	...
                case PERF_RECORD_MISC_GUEST_USER:
                        ++top->guest_us_samples;
                        /*
                         * TODO: we don't process guest user from host side
                         * except simple counting.
                         */
                        /* Fall thru */
                default:
                        continue;
                }
	...
}

2) With other subcommands, it seems perf would drop guest user space statistics. Sorry
for my old memory.

> 
> > event->ip.pid is equal to machine->pid only when
> > ((event->header.misc & PERF_RECORD_MISC_CPUMODE_MASK) == PERF_RECORD_MISC_GUEST_KERNEL).
> >
> > In function perf_event__inject_buildid, we shouldn't reset machine->pid to
> > event->ip.pid. They are equal to each other if it's a guest os event. Isn't it?
> 
> I have not tried capturing samples on a kvm process. So I don't know.
There is a local team here working on performance tuning/benchmarking. They
use 'perf kvm' to collect/analyze their guest os performance.



  reply	other threads:[~2012-02-03  3:30 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-01-13 14:47 [PATCH] perf: fix broken perf inject -b Stephane Eranian
2012-01-13 16:53 ` Arnaldo Carvalho de Melo
2012-01-13 16:54   ` Stephane Eranian
2012-01-16 18:53     ` Stephane Eranian
2012-01-30 19:00       ` Arnaldo Carvalho de Melo
2012-01-30 19:53         ` Stephane Eranian
2012-01-30 20:04           ` Arnaldo Carvalho de Melo
2012-01-30 20:09             ` Stephane Eranian
2012-01-30 20:36               ` Arnaldo Carvalho de Melo
2012-01-31  5:58                 ` Yanmin Zhang
2012-02-02 11:22                   ` Stephane Eranian
2012-02-03  3:30                     ` Yanmin Zhang [this message]
2012-01-26 14:16     ` Stephane Eranian
2012-01-26 14:23       ` Arnaldo Carvalho de Melo

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