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Subject[patch 2/4] x86,perf: P4 PMU -- protect sensible procedures from preemption
Steven reported
|
| I'm getting:
|
| Pid: 3477, comm: perf Not tainted 2.6.34-rc6 #2727
| Call Trace:
| [<ffffffff811c7565>] debug_smp_processor_id+0xd5/0xf0
| [<ffffffff81019874>] p4_hw_config+0x2b/0x15c
| [<ffffffff8107acbc>] ? trace_hardirqs_on_caller+0x12b/0x14f
| [<ffffffff81019143>] hw_perf_event_init+0x468/0x7be
| [<ffffffff810782fd>] ? debug_mutex_init+0x31/0x3c
| [<ffffffff810c68b2>] T.850+0x273/0x42e
| [<ffffffff810c6cab>] sys_perf_event_open+0x23e/0x3f1
| [<ffffffff81009e6a>] ? sysret_check+0x2e/0x69
| [<ffffffff81009e32>] system_call_fastpath+0x16/0x1b
|
| When running perf record in latest tip/perf/core
|

Due to the fact that p4 counters are shared between HT threads
we synthetically divide the whole set of counters into two
non-intersected subsets. And while we're "borrowing" counters
from these subsets we should not be preempted (well, strictly
speaking in p4_hw_config we just pre-set reference to the
subset which allow to save some cycles in schedule routine
if it happens on the same cpu). So use get_cpu/put_cpu pair.

Also p4_pmu_schedule_events should use smp_processor_id rather
than raw_ version. This allow us to catch up preemption issue
(if there will ever be).

Reported-by: Steven Rostedt <rostedt@goodmis.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Ingo Molnar <mingo@elte.hu>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
---
Note: I've removed Steven's Tested-by tag, since due to
commit 9d0fcba67e47ff398a6fa86476d4884d472dc98a the former
patch Steven were testing is not applicable anymore.

arch/x86/kernel/cpu/perf_event_p4.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
=====================================================================
--- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c
+++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
@@ -421,7 +421,8 @@ static u64 p4_pmu_event_map(int hw_event

static int p4_hw_config(struct perf_event *event)
{
- int cpu = raw_smp_processor_id();
+ int cpu = get_cpu();
+ int rc = 0;
u32 escr, cccr;

/*
@@ -454,7 +455,10 @@ static int p4_hw_config(struct perf_even
p4_config_pack_cccr(P4_CCCR_MASK_HT));
}

- return x86_setup_perfctr(event);
+ rc = x86_setup_perfctr(event);
+ put_cpu();
+
+ return rc;
}

static inline void p4_pmu_clear_cccr_ovf(struct hw_perf_event *hwc)


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