[tip:perfcounters/core] perf_counter: x86: Disallow interval of 1

tip-bot for Ingo Molnar
2009-05-15T08:47:32Z

Commit-ID: 1c80f4b598d9b075a2a0be694e28be93a6702bcc
Gitweb: http://git.kernel.org/tip/1c80f4b598d9b075a2a0be694e28be93a6702bcc
Author: Ingo Molnar <mingo@elte.hu>
AuthorDate: Fri, 15 May 2009 08:25:22 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 15 May 2009 09:47:05 +0200

perf_counter: x86: Disallow interval of 1

On certain CPUs i have observed a stuck PMU if interval was set to
1 and NMIs were used. The PMU had PMC0 set in MSR_CORE_PERF_GLOBAL_STATUS,
but it was not possible to ack it via MSR_CORE_PERF_GLOBAL_OVF_CTRL,
and the NMI loop got stuck infinitely.

[ Impact: fix rare hangs during high perfcounter load ]

Signed-off-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 | 5 +++++
1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 1dcf670..46a82d1 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -473,6 +473,11 @@ x86_perf_counter_set_period(struct perf_counter *counter,
left += period;
atomic64_set(&hwc->period_left, left);
}
+ /*
+ * Quirk: certain CPUs dont like it if just 1 event is left:
+ */
+ if (unlikely(left < 2))
+ left = 2;

per_cpu(prev_left[idx], smp_processor_id()) = left;