Re: [PATCH 2/2] powerpc/perf: Fix the threshold compare group constraint for power9

[Athira Rajeev <atrajeev@linux.vnet.ibm.com>]

> On 06-May-2022, at 11:40 AM, Kajol Jain <kjain@linux.ibm.com> wrote:
> 
> Thresh compare bits for a event is used to program thresh compare
> field in Monitor Mode Control Register A (MMCRA: 9-18 bits for power9).
> When scheduling events as a group, all events in that group should
> match value in threshold bits (like thresh compare, thresh control,
> thresh select). Otherwise event open for the sibling events should fail.
> But in the current code, incase thresh compare bits are not valid,
> we are not failing in group_constraint function which can result
> in invalid group schduling.
> 
> Fix the issue by returning -1 incase event is threshold and threshold
> compare value is not valid.
> 
> Thresh control bits in the event code is used to program thresh_ctl
> field in Monitor Mode Control Register A (MMCRA: 48-55). In below example,
> the scheduling of group events PM_MRK_INST_CMPL (873534401e0) and
> PM_THRESH_MET (8734340101ec) is expected to fail as both event
> request different thresh control bits and invalid thresh compare value.
> 
> Result before the patch changes:
> 
> [command]# perf stat -e "{r8735340401e0,r8734340101ec}" sleep 1
> 
> Performance counter stats for 'sleep 1':
> 
>            11,048      r8735340401e0
>             1,967      r8734340101ec
> 
>       1.001354036 seconds time elapsed
> 
>       0.001421000 seconds user
>       0.000000000 seconds sys
> 
> Result after the patch changes:
> 
> [command]# perf stat -e "{r8735340401e0,r8734340101ec}" sleep 1
> Error:
> The sys_perf_event_open() syscall returned with 22 (Invalid argument)
> for event (r8735340401e0).
> /bin/dmesg | grep -i perf may provide additional information.
> 
> Fixes: 78a16d9fc1206 ("powerpc/perf: Avoid FAB_*_MATCH checks for power9")
> Signed-off-by: Kajol Jain <kjain@linux.ibm.com>

Reviewed-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>

Thanks
Athira
> ---
> arch/powerpc/perf/isa207-common.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/perf/isa207-common.c b/arch/powerpc/perf/isa207-common.c
> index 013b06af6fe6..bb5d64862bc9 100644
> --- a/arch/powerpc/perf/isa207-common.c
> +++ b/arch/powerpc/perf/isa207-common.c
> @@ -508,7 +508,8 @@ int isa207_get_constraint(u64 event, unsigned long *maskp, unsigned long *valp,
> 		if (event_is_threshold(event) && is_thresh_cmp_valid(event)) {
> 			mask  |= CNST_THRESH_MASK;
> 			value |= CNST_THRESH_VAL(event >> EVENT_THRESH_SHIFT);
> -		}
> +		} else if (event_is_threshold(event))
> +			return -1;
> 	} else {
> 		/*
> 		 * Special case for PM_MRK_FAB_RSP_MATCH and PM_MRK_FAB_RSP_MATCH_CYC,
> -- 
> 2.31.1
>