linux-kernel - Re: [PATCH] perf kvm record/report: 'unprocessable sample' error while recording/reporting guest data

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Date:	Thu, 17 Dec 2015 09:48:03 +0530
From:	Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:	acme@...nel.org
Cc:	linux-kernel@...r.kernel.org, naveen.n.rao@...ux.vnet.ibm.com
Subject: Re: [PATCH] perf kvm record/report: 'unprocessable sample' error
 while recording/reporting guest data

Hi acme,

I sent this patch few days ago. Unfortunately nobody has payed attention.

Can you please pick this up.

Regards,
Ravi

On Monday 07 December 2015 12:25 PM, Ravi Bangoria wrote:
> While recording guest samples in host using perf kvm record, it will
> populate unprocessable sample error, though samples will be recorded
> properly. While generating report using perf kvm report, no samples will
> be processed and same error will populate. We have seen this behaviour
> with upstream perf(4.4-rc3) on x86 and ppc64 hardware.
>
> Reason behind this failure is, when it tries to fetch machine from rb_tree
> of machines, it fails. As a part of tracing a bug, we figured out that this
> code was incorrectly refactored in commit 54245fdc357613633954bfd38cffb71cb9def067
> ("perf session: Remove wrappers to machines__find")
>
> This patch will change the functionality such that if it can't fetch
> machine in first trial, it will create one node of machine and add that to
> rb_tree. So next time when it tries to fetch same machine from rb_tree,
> it won't fail. Actually it was the case before refactoring of code in
> aforementioned commit.
>
> This patch is generated from acme perf/core branch.
>
> Below I've mention an example that demonstrate the behaviour before and
> after applying patch.
>
> Before applying patch:
> [Note: One needs to run guest before recording data in host]
>
> ravi@...i-bangoria:~$ ./perf kvm record -a
> Warning:
> 5903 unprocessable samples recorded.
> Do you have a KVM guest running and not using 'perf kvm'?
> [ perf record: Captured and wrote 1.409 MB perf.data.guest (285 samples) ]
>
> ravi@...i-bangoria:~$ ./perf kvm report --stdio
> Warning:
> 5903 unprocessable samples recorded.
> Do you have a KVM guest running and not using 'perf kvm'?
> # To display the perf.data header info, please use --header/--header-only options.
> #
> #
> # Total Lost Samples: 0
> #
> # Samples: 285  of event 'cycles'
> # Event count (approx.): 88715406
> #
> # Overhead  Command  Shared Object  Symbol
> # ........  .......  .............  ......
> #
>
> #
> # (For a higher level overview, try: perf report --sort comm,dso)
> #
>
> After applying patch:
>
> ravi@...i-bangoria:~$ ./perf kvm record -a
> [ perf record: Captured and wrote 1.188 MB perf.data.guest (17 samples) ]
>
> ravi@...i-bangoria:~$ ./perf kvm report --stdio
> # To display the perf.data header info, please use --header/--header-only options.
> #
> #
> # Total Lost Samples: 0
> #
> # Samples: 17  of event 'cycles'
> # Event count (approx.): 700746
> #
> # Overhead  Command  Shared Object     Symbol
> # ........  .......  ................  ......................
> #
>      34.19%  :5758    [unknown]         [g] 0xffffffff818682ab
>      22.79%  :5758    [unknown]         [g] 0xffffffff812dc7f8
>      22.79%  :5758    [unknown]         [g] 0xffffffff818650d0
>      14.83%  :5758    [unknown]         [g] 0xffffffff8161a1b6
>       2.49%  :5758    [unknown]         [g] 0xffffffff818692bf
>       0.48%  :5758    [unknown]         [g] 0xffffffff81869253
>       0.05%  :5758    [unknown]         [g] 0xffffffff81869250
>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
> ---
>   tools/perf/util/session.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index c35ffdd..468de95 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -972,7 +972,7 @@ static struct machine *machines__find_for_cpumode(struct machines *machines,
>
>   		machine = machines__find(machines, pid);
>   		if (!machine)
> -			machine = machines__find(machines, DEFAULT_GUEST_KERNEL_ID);
> +			machine = machines__findnew(machines, DEFAULT_GUEST_KERNEL_ID);
>   		return machine;
>   	}
>

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