On 04/11/15 18:28, Mark Rutland wrote:
On Tue, Oct 20, 2015 at 02:05:25PM +0100, Suzuki K. Poulose wrote:
Adds helper routines to manipulate the counter controls for
all the counters on the CCI PMU.
pmu_disable_counters_ctrl: Iterates over the counters,
checking the status of each counter and disabling any enabled
counters. For each such changed counter, the mask is updated so that
one can restore the state later using pmu_enable_counters_ctrl.
/*
+ * Restore the status of the counters.
+ * For each counter set in the mask, enable the counter back.
+ */
+static void pmu_restore_counters_ctrl(struct cci_pmu *cci_pmu, unsigned long
*mask)
+{
+ int i;
+
+ for_each_set_bit(i, mask, cci_pmu->num_cntrs)
+ pmu_enable_counter(cci_pmu, i);
+}
+
+/*
+ * For all counters on the CCI-PMU, disable any 'enabled' counters,
+ * saving the changed counters in the mask, so that we can restore
+ * it later using pmu_restore_counters_ctrl.
+ */
+static void pmu_disable_counters_ctrl(struct cci_pmu *cci_pmu, unsigned long
*mask)
+{
+ int i;
+
+ for (i = 0; i < cci_pmu->num_cntrs; i++) {
+ clear_bit(i, mask);
+ if (pmu_get_counter_ctrl(cci_pmu, i)) {
+ set_bit(i, mask);
+ pmu_disable_counter(cci_pmu, i);
+ }
+ }
+}
I don't understand what's going on with the mask here. Why do we clear
ieach bit when the only user (introduced in the next patch) explicitly
clears the mask anyway?
To be more precise, it should have been :
if (pmu_get_counter_ctrl(cci_pmu, i)) {
set_bit(i, mask);
pmu_disable_counter(cci_pmu, i);
} else
clear_bit(i, mask);
Can we not get rid of the mask entirely? The combination of used_mask
and each event's hwc->state tells us which counters are actually in use.
The problem is that neither hwc->state nor the cci_pmu->hw_events->events is
protected by pmu_lock, while enable/disable counter is. So we cannot really
rely on ((struct perf_event *)(cci_pmu->hw_events->events[counter]))->hw->state.
What we do above is, create a mask of the counters which are enabled at the
moment and disable all of them. We then program the counter and then re-enable
those which were enabled (as marked in the mask).
Suzuki
Thanks,
Mark.
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