From: Anshuman Khandual <khandual@linux.vnet.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@ozlabs.org
Subject: Re: [PATCH] powerpc, perf: Configure BHRB filter before enabling PMU interrupts
Date: Wed, 18 Dec 2013 09:11:38 +0530 [thread overview]
Message-ID: <52B11972.6030206@linux.vnet.ibm.com> (raw)
In-Reply-To: <1387332893-14407-1-git-send-email-mpe@ellerman.id.au>
On 12/18/2013 07:44 AM, Michael Ellerman wrote:
> From: Anshuman Khandual <khandual@linux.vnet.ibm.com>
>
> Right now the config_bhrb() PMU specific call happens after
> write_mmcr0(), which actually enables the PMU for event counting and
> interrupts. So there is a small window of time where the PMU and BHRB
> runs without the required HW branch filter (if any) enabled in BHRB.
>
> This can cause some of the branch samples to be collected through BHRB
> without any filter applied and hence affects the correctness of
> the results. This patch moves the BHRB config function call before
> enabling interrupts.
>
> Here are some data points captured via trace prints which depicts how we
> could get PMU interrupts with BHRB filter NOT enabled with a standard
> perf record command line (asking for branch record information as well).
>
> $ perf record -j any_call ls
>
> Before the patch:-
>
> ls-1962 [003] d... 2065.299590: .perf_event_interrupt: MMCRA: 40000000000
> ls-1962 [003] d... 2065.299603: .perf_event_interrupt: MMCRA: 40000000000
> ...
>
> All the PMU interrupts before this point did not have the requested
> HW branch filter enabled in the MMCRA.
>
> ls-1962 [003] d... 2065.299647: .perf_event_interrupt: MMCRA: 40040000000
> ls-1962 [003] d... 2065.299662: .perf_event_interrupt: MMCRA: 40040000000
>
> After the patch:-
>
> ls-1850 [008] d... 190.311828: .perf_event_interrupt: MMCRA: 40040000000
> ls-1850 [008] d... 190.311848: .perf_event_interrupt: MMCRA: 40040000000
>
> All the PMU interrupts have the requested HW BHRB branch filter
> enabled in MMCRA.
>
> Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
> [mpe: Fixed up whitespace and cleaned up changelog]
Thanks Michael for cleaning and resending this out.
next prev parent reply other threads:[~2013-12-18 3:42 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-18 2:14 [PATCH] powerpc, perf: Configure BHRB filter before enabling PMU interrupts Michael Ellerman
2013-12-18 3:41 ` Anshuman Khandual [this message]
-- strict thread matches above, loose matches on Subject: below --
2013-10-07 4:30 Anshuman Khandual
2013-10-08 4:21 ` Michael Ellerman
2013-10-08 7:21 ` Anshuman Khandual
2013-10-09 1:21 ` Michael Ellerman
2013-10-09 4:46 ` Anshuman Khandual
2013-10-09 6:03 ` Michael Ellerman
2013-10-10 8:50 ` Anshuman Khandual
2013-10-11 2:11 ` Michael Ellerman
2013-10-11 4:32 ` Anshuman Khandual
2013-10-14 6:19 ` Michael Ellerman
2013-10-16 4:30 ` Anshuman Khandual
2013-12-13 6:46 ` Anshuman Khandual
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