From: Nicholas Piggin <npiggin@gmail.com>
To: linuxppc-dev@lists.ozlabs.org
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>,
Madhavan Srinivasan <maddy@linux.ibm.com>,
Nicholas Piggin <npiggin@gmail.com>
Subject: [PATCH] powerpc/64s/perf: Always use SIAR for kernel interrupts
Date: Wed, 21 Jul 2021 00:15:04 +1000 [thread overview]
Message-ID: <20210720141504.420110-1-npiggin@gmail.com> (raw)
If an interrupt is taken in kernel mode, always use SIAR for it rather than
looking at regs_sipr. This prevents samples piling up around interrupt
enable (hard enable or interrupt replay via soft enable) in PMUs / modes
where the PR sample indication is not in synch with SIAR.
This results in better sampling of interrupt entry and exit in particular.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
arch/powerpc/perf/core-book3s.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index bb0ee716de91..91203ed9d0ff 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -340,6 +340,13 @@ static inline void perf_read_regs(struct pt_regs *regs)
* If the PMU doesn't update the SIAR for non marked events use
* pt_regs.
*
+ * If regs is a kernel interrupt, always use SIAR. Some PMUs have an
+ * issue with regs_sipr not being in synch with SIAR in interrupt entry
+ * and return sequences, which can result in regs_sipr being true for
+ * kernel interrupts and SIAR, which has the effect of causing samples
+ * to pile up at mtmsrd MSR[EE] 0->1 or pending irq replay around
+ * interrupt entry/exit.
+ *
* If the PMU has HV/PR flags then check to see if they
* place the exception in userspace. If so, use pt_regs. In
* continuous sampling mode the SIAR and the PMU exception are
@@ -356,6 +363,8 @@ static inline void perf_read_regs(struct pt_regs *regs)
use_siar = 1;
else if ((ppmu->flags & PPMU_NO_CONT_SAMPLING))
use_siar = 0;
+ else if (!user_mode(regs))
+ use_siar = 1;
else if (!(ppmu->flags & PPMU_NO_SIPR) && regs_sipr(regs))
use_siar = 0;
else
--
2.23.0
next reply other threads:[~2021-07-20 14:15 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-20 14:15 Nicholas Piggin [this message]
2021-07-21 5:36 ` [PATCH] powerpc/64s/perf: Always use SIAR for kernel interrupts Athira Rajeev
2021-08-18 13:38 ` Michael Ellerman
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