From 7caaf4d8241feecafb87919402b0a6dbb1b71d9e Mon Sep 17 00:00:00 2001 From: Robert Richter Date: Mon, 2 Apr 2012 20:19:15 +0200 Subject: [PATCH] perf/x86-ibs: Extend hw period that triggers overflow If the last hw period is too short we might hit the irq handler which biases the results. Thus try to have a max last period that triggers the sw overflow. Signed-off-by: Robert Richter Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/1333390758-10893-10-git-send-email-robert.richter@amd.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/perf_event_amd_ibs.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/perf_event_amd_ibs.c b/arch/x86/kernel/cpu/perf_event_amd_ibs.c index 3e32908292a7..cb51a3e55870 100644 --- a/arch/x86/kernel/cpu/perf_event_amd_ibs.c +++ b/arch/x86/kernel/cpu/perf_event_amd_ibs.c @@ -85,8 +85,19 @@ perf_event_set_period(struct hw_perf_event *hwc, u64 min, u64 max, u64 *hw_perio overflow = 1; } - if (left > max) - left = max; + /* + * If the hw period that triggers the sw overflow is too short + * we might hit the irq handler. This biases the results. + * Thus we shorten the next-to-last period and set the last + * period to the max period. + */ + if (left > max) { + left -= max; + if (left > max) + left = max; + else if (left < min) + left = min; + } *hw_period = (u64)left;