Re: [PATCH] Powerpc/perf: Wire up PMI throttling
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2018-11-15 12:43:45
Also in:
lkml
Ravi Bangoria [off-list ref] writes:
Commit 14c63f17b1fde ("perf: Drop sample rate when sampling is too
slow") introduced a way to throttle PMU interrupts if we're spending
too much time just processing those. Wire up powerpc PMI handler to
use this infrastructure.To be clear we have throttling of the *rate* of interrupts, but this adds throttling based on the *time taken* to process the interrupts. Or at least that's my understanding?
quoted hunk ↗ jump to hunk
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c index 9a86572db1ef..44f85fa22356 100644 --- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c@@ -18,6 +18,7 @@ #include <linux/errno.h> #include <linux/sched.h> #include <linux/sched/debug.h> +#include <linux/sched/clock.h> #include <linux/kernel.h> #include <linux/mm.h> #include <linux/pkeys.h>@@ -1803,9 +1804,12 @@ void vsx_unavailable_tm(struct pt_regs *regs) void performance_monitor_exception(struct pt_regs *regs) { + u64 start_clock; __this_cpu_inc(irq_stat.pmu_irqs); + start_clock = sched_clock(); perf_irq(regs); + perf_sample_event_took(sched_clock() - start_clock); }
Despite the name, perf_irq() may not actually be the perf IRQ handler :) It's a function pointer which might call perf or might call oprofile, or a dummy handler. I don't think we should be calling perf_sample_event_took() if we're not actually using perf, that is wasteful at best. So the timing logic should go in the perf specific handler I think. ie. perf_event_interrupt(). cheers