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    Subject[PATCH 4.14 36/95] powerpc/perf: Record counter overflow always if SAMPLE_IP is unset
    Date
    From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    From: Athira Rajeev <atrajeev@linux.vnet.ibm.com>

    [ Upstream commit d137845c973147a22622cc76c7b0bc16f6206323 ]

    While sampling for marked events, currently we record the sample only
    if the SIAR valid bit of Sampled Instruction Event Register (SIER) is
    set. SIAR_VALID bit is used for fetching the instruction address from
    Sampled Instruction Address Register(SIAR). But there are some
    usecases, where the user is interested only in the PMU stats at each
    counter overflow and the exact IP of the overflow event is not
    required. Dropping SIAR invalid samples will fail to record some of
    the counter overflows in such cases.

    Example of such usecase is dumping the PMU stats (event counts) after
    some regular amount of instructions/events from the userspace (ex: via
    ptrace). Here counter overflow is indicated to userspace via signal
    handler, and captured by monitoring and enabling I/O signaling on the
    event file descriptor. In these cases, we expect to get
    sample/overflow indication after each specified sample_period.

    Perf event attribute will not have PERF_SAMPLE_IP set in the
    sample_type if exact IP of the overflow event is not requested. So
    while profiling if SAMPLE_IP is not set, just record the counter
    overflow irrespective of SIAR_VALID check.

    Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
    [mpe: Reflow comment and if formatting]
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/1612516492-1428-1-git-send-email-atrajeev@linux.vnet.ibm.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/powerpc/perf/core-book3s.c | 19 +++++++++++++++----
    1 file changed, 15 insertions(+), 4 deletions(-)

    diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
    index 56f16c803590..2669847434b8 100644
    --- a/arch/powerpc/perf/core-book3s.c
    +++ b/arch/powerpc/perf/core-book3s.c
    @@ -2055,7 +2055,17 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
    left += period;
    if (left <= 0)
    left = period;
    - record = siar_valid(regs);
    +
    + /*
    + * If address is not requested in the sample via
    + * PERF_SAMPLE_IP, just record that sample irrespective
    + * of SIAR valid check.
    + */
    + if (event->attr.sample_type & PERF_SAMPLE_IP)
    + record = siar_valid(regs);
    + else
    + record = 1;
    +
    event->hw.last_period = event->hw.sample_period;
    }
    if (left < 0x80000000LL)
    @@ -2073,9 +2083,10 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
    * MMCR2. Check attr.exclude_kernel and address to drop the sample in
    * these cases.
    */
    - if (event->attr.exclude_kernel && record)
    - if (is_kernel_addr(mfspr(SPRN_SIAR)))
    - record = 0;
    + if (event->attr.exclude_kernel &&
    + (event->attr.sample_type & PERF_SAMPLE_IP) &&
    + is_kernel_addr(mfspr(SPRN_SIAR)))
    + record = 0;

    /*
    * Finally record data if requested.
    --
    2.30.1


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