[tip:perfcounters/core] perf_counter: x86: Fix throttling

tip-bot for Ingo Molnar
2009-05-15T08:45:28Z

Commit-ID: f5a5a2f6e69e88647ae12da39f0ff3a510bcf0a6
Gitweb: http://git.kernel.org/tip/f5a5a2f6e69e88647ae12da39f0ff3a510bcf0a6
Author: Ingo Molnar <mingo@elte.hu>
AuthorDate: Wed, 13 May 2009 12:54:01 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 15 May 2009 09:46:56 +0200

perf_counter: x86: Fix throttling

If counters are disabled globally when a perfcounter IRQ/NMI hits,
and if we throttle in that case, we'll promote the '0' value to
the next lapic IRQ and disable all perfcounters at that point,
permanently ...

Fix it.

[ Impact: fix hung perfcounters under load ]

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
arch/x86/kernel/cpu/perf_counter.c | 20 +++++++++++++++-----
1 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 3a92a2b..88ae8ce 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -765,8 +765,13 @@ out:
/*
* Restore - do not reenable when global enable is off or throttled:
*/
- if (++cpuc->interrupts < PERFMON_MAX_INTERRUPTS)
- intel_pmu_restore_all(cpuc->throttle_ctrl);
+ if (cpuc->throttle_ctrl) {
+ if (++cpuc->interrupts < PERFMON_MAX_INTERRUPTS) {
+ intel_pmu_restore_all(cpuc->throttle_ctrl);
+ } else {
+ pr_info("CPU#%d: perfcounters: max interrupt rate exceeded! Throttle on.\n", smp_processor_id());
+ }
+ }

return ret;
}
@@ -817,11 +822,16 @@ void perf_counter_unthrottle(void)

cpuc = &__get_cpu_var(cpu_hw_counters);
if (cpuc->interrupts >= PERFMON_MAX_INTERRUPTS) {
- if (printk_ratelimit())
- printk(KERN_WARNING "perfcounters: max interrupts exceeded!\n");
+ pr_info("CPU#%d: perfcounters: throttle off.\n", smp_processor_id());
+
+ /*
+ * Clear them before re-enabling irqs/NMIs again:
+ */
+ cpuc->interrupts = 0;
hw_perf_restore(cpuc->throttle_ctrl);
+ } else {
+ cpuc->interrupts = 0;
}
- cpuc->interrupts = 0;
}

void smp_perf_counter_interrupt(struct pt_regs *regs)