perf/x86-ibs: Fix frequency profiling

Fixing profiling at a fixed frequency, in this case the freq value and
sample period was setup incorrectly. Since sampling periods are
adjusted we also allow periods that have lower 4 bits set.

Another fix is the setup of the hw counter: If we modify
hwc->sample_period, we also need to update hwc->last_period and
hwc->period_left.

Signed-off-by: Robert Richter <robert.richter@amd.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1333390758-10893-5-git-send-email-robert.richter@amd.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 16 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 ebf169fe40ef..bc401bd9f14a 100644
--- a/arch/x86/kernel/cpu/perf_event_amd_ibs.c
+++ b/arch/x86/kernel/cpu/perf_event_amd_ibs.c
@@ -162,9 +162,16 @@ static int perf_ibs_init(struct perf_event *event)
                 if (config & perf_ibs->cnt_mask)
                         /* raw max_cnt may not be set */
                         return -EINVAL;
-                if (hwc->sample_period & 0x0f)
-                        /* lower 4 bits can not be set in ibs max cnt */
+                if (!event->attr.sample_freq && hwc->sample_period & 0x0f)
+                        /*
+                         * lower 4 bits can not be set in ibs max cnt,
+                         * but allowing it in case we adjust the
+                         * sample period to set a frequency.
+                         */
                         return -EINVAL;
+                hwc->sample_period &= ~0x0FULL;
+                if (!hwc->sample_period)
+                        hwc->sample_period = 0x10;
         } else {
                 max_cnt = config & perf_ibs->cnt_mask;
                 config &= ~perf_ibs->cnt_mask;
@@ -175,6 +182,13 @@ static int perf_ibs_init(struct perf_event *event)
         if (!hwc->sample_period)
                 return -EINVAL;
 
+        /*
+         * If we modify hwc->sample_period, we also need to update
+         * hwc->last_period and hwc->period_left.
+         */
+        hwc->last_period = hwc->sample_period;
+        local64_set(&hwc->period_left, hwc->sample_period);
+
         hwc->config_base = perf_ibs->msr;
         hwc->config = config;