Re: [PATCH v2 2/2] powerpc/perf: Return regs->nip as instruction pointer value when SIAR is 0
From: Christophe Leroy <hidden>
Date: 2021-08-13 09:35:05
Le 13/08/2021 à 10:24, Kajol Jain a écrit :
Incase of random sampling, there can be scenarios where SIAR is not latching sample address and results in 0 value. Since current code directly returning the siar value, we could see multiple instruction pointer values as 0 in perf report. Patch resolves this issue by adding a ternary condition to return regs->nip incase SIAR is 0.
Your description seems rather similar to https://github.com/linuxppc/linux/commit/2ca13a4cc56c920a6c9fc8ee45d02bccacd7f46c Does it mean that the problem occurs on more than the power10 DD1 ? In that case, can the solution be common instead of doing something for power10 DD1 and something for others ?
quoted hunk ↗ jump to hunk
Fixes: 75382aa72f06 ("powerpc/perf: Move code to select SIAR or pt_regs into perf_read_regs") Signed-off-by: Kajol Jain <redacted> --- arch/powerpc/perf/core-book3s.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c index 1b464aad29c4..aeecaaf6810f 100644 --- a/arch/powerpc/perf/core-book3s.c +++ b/arch/powerpc/perf/core-book3s.c@@ -2260,7 +2260,7 @@ unsigned long perf_instruction_pointer(struct pt_regs *regs) else return regs->nip; } else if (use_siar && siar_valid(regs)) - return siar + perf_ip_adjust(regs); + return siar ? siar + perf_ip_adjust(regs) : regs->nip; else if (use_siar) return 0; // no valid instruction pointer else