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powerpc/64s/perf: Always use SIAR for kernel interrupts

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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>
Tested-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210720141504.420110-1-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2021-07-21 00:15:04 +10:00 committed by Michael Ellerman
parent e9ef81e107
commit cf9c615cde
1 changed files with 9 additions and 0 deletions
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9
arch/powerpc/perf/core-book3s.c
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@ -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