Messages in this thread | | | Date | Wed, 5 May 2010 18:57:34 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH -tip] x86,perf: P4 PMU -- protect sensible procedures from preemption |
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On Wed, May 05, 2010 at 07:07:40PM +0400, Cyrill Gorcunov wrote: > 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. So use > get_cpu/put_cpu pair. > > Reported-by: Steven Rostedt <rostedt@goodmis.org> > Tested-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> > Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org> > --- > arch/x86/kernel/cpu/perf_event_p4.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 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 +421,7 @@ 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(); > u32 escr, cccr; > > /* > @@ -440,7 +440,7 @@ static int p4_hw_config(struct perf_even > event->hw.config = p4_set_ht_bit(event->hw.config); > > if (event->attr.type != PERF_TYPE_RAW) > - return 0; > + goto out; > > /* > * We don't control raw events so it's up to the caller > @@ -455,6 +455,8 @@ static int p4_hw_config(struct perf_even > (p4_config_pack_escr(P4_ESCR_MASK_HT) | > p4_config_pack_cccr(P4_CCCR_MASK_HT)); > > +out: > + put_cpu(); > return 0; > } > > @@ -741,7 +743,7 @@ static int p4_pmu_schedule_events(struct > { > unsigned long used_mask[BITS_TO_LONGS(X86_PMC_IDX_MAX)]; > unsigned long escr_mask[BITS_TO_LONGS(ARCH_P4_TOTAL_ESCR)]; > - int cpu = raw_smp_processor_id(); > + int cpu = get_cpu(); > struct hw_perf_event *hwc; > struct p4_event_bind *bind; > unsigned int i, thread, num; > @@ -777,6 +779,7 @@ reserve: > } > > done: > + put_cpu(); > return num ? -ENOSPC : 0; > }
That's no big deal. But I think the schedule_events() is called on pmu::enable() time, when preemption is already disabled.
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