x86, perf_counter, bts: Fail if BTS is not available

Reserve PERF_COUNT_HW_BRANCH_INSTRUCTIONS with sample_period ==
1 for BTS tracing and fail, if BTS is not available.

Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090902140612.943801000@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 11 insertions, 14 deletions

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 396e35db705..2f41874ffb8 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -769,7 +769,7 @@ static int reserve_bts_hardware(void)
         int cpu, err = 0;
 
         if (!bts_available())
-                return -EOPNOTSUPP;
+                return 0;
 
         get_online_cpus();
 
@@ -914,7 +914,7 @@ static int __hw_perf_counter_init(struct perf_counter *counter)
                         if (!reserve_pmc_hardware())
                                 err = -EBUSY;
                         else
-                                reserve_bts_hardware();
+                                err = reserve_bts_hardware();
                 }
                 if (!err)
                         atomic_inc(&active_counters);
@@ -979,6 +979,13 @@ static int __hw_perf_counter_init(struct perf_counter *counter)
         if (config == -1LL)
                 return -EINVAL;
 
+        /*
+         * Branch tracing:
+         */
+        if ((attr->config == PERF_COUNT_HW_BRANCH_INSTRUCTIONS) &&
+            (hwc->sample_period == 1) && !bts_available())
+                return -EOPNOTSUPP;
+
         hwc->config |= config;
 
         return 0;
@@ -1355,19 +1362,9 @@ static int x86_pmu_enable(struct perf_counter *counter)
 
         idx = fixed_mode_idx(counter, hwc);
         if (idx == X86_PMC_IDX_FIXED_BTS) {
-                /*
-                 * Try to use BTS for branch tracing. If that is not
-                 * available, try to get a generic counter.
-                 */
-                if (unlikely(!cpuc->ds))
-                        goto try_generic;
-
-                /*
-                 * Try to get the fixed counter, if that is already taken
-                 * then try to get a generic counter:
-                 */
+                /* BTS is already occupied. */
                 if (test_and_set_bit(idx, cpuc->used_mask))
-                        goto try_generic;
+                        return -EAGAIN;
 
                 hwc->config_base        = 0;
                 hwc->counter_base       = 0;