Re: [PATCH 1/3] powerpc/perf: Fix branch_filter support for multiple filters in powerpc

[Disha Goel <disgoel@linux.ibm.com>]

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On 9/13/22 5:25 PM, Athira Rajeev wrote:
> For PERF_SAMPLE_BRANCH_STACK sample type, different branch_sample_type
> ie branch filters are supported. The branch filters are requested via
> event attribute "branch_sample_type". Multiple branch filters can be
> passed in event attribute.
>
> Example:
> perf record -b -o- -B --branch-filter any,ind_call true
>
> Powerpc does not support having multiple branch filters at
> sametime. In powerpc, branch filters for branch stack sampling
> is set via MMCRA IFM bits [32:33]. But currently when requesting
> for multiple filter types, the "perf record" command does not
> report any error.
>
> Example:
> perf record -b -o- -B --branch-filter any,save_type true
> perf record -b -o- -B --branch-filter any,ind_call true
>
> The "bhrb_filter_map" function in PMU driver code does the
> validity check for supported branch filters. But this check
> is done for single filter. Hence "perf record" will proceed
> here without reporting any error.
>
> Fix power_pmu_event_init to return EOPNOTSUPP when multiple
> branch filters are requested in the event attr.
>
> After the fix:
> perf record --branch-filter any,ind_call -- ls
> Error:
> cycles: PMU Hardware doesn't support sampling/overflow-interrupts.
> Try 'perf stat'
>
> Reported-by: Disha Goel<disgoel@linux.vnet.ibm.com>
> Signed-off-by: Athira Rajeev<atrajeev@linux.vnet.ibm.com>
> Reviewed-by: Madhavan Srinivasan<maddy@linux.ibm.com>

Tested-by: Disha Goel<disgoel@linux.vnet.ibm.com>

> ---
>   arch/powerpc/perf/core-book3s.c | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index 13919eb96931..2c2d235cb8d8 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -2131,6 +2131,21 @@ static int power_pmu_event_init(struct perf_event *event)
>   	if (has_branch_stack(event)) {
>   		u64 bhrb_filter = -1;
>
> +		/*
> +		 * powerpc does not support having multiple branch filters
> +		 * at sametime. Branch filters are set via MMCRA IFM[32:33]
> +		 * bits for power8 and above. Return EOPNOTSUPP when multiple
> +		 * branch filters are requested in the event attr.
> +		 *
> +		 * When opening event via perf_event_open, branch_sample_type
> +		 * gets adjusted in perf_copy_attr function. Kernel will
> +		 * automatically adjust the branch_sample_type based on the
> +		 * event modifier settings to include PERF_SAMPLE_BRANCH_PLM_ALL.
> +		 * Hence drop the check for PERF_SAMPLE_BRANCH_PLM_ALL.
> +		 */
> +		if (hweight64(event->attr.branch_sample_type & ~PERF_SAMPLE_BRANCH_PLM_ALL) > 1)
> +			return -EOPNOTSUPP;
> +
>   		if (ppmu->bhrb_filter_map)
>   			bhrb_filter = ppmu->bhrb_filter_map(
>   					event->attr.branch_sample_type);

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