Commit-ID: 9e7eaac95af6c1aecaf558b8c7a1757d5f2d2ad7 Gitweb: http://git.kernel.org/tip/9e7eaac95af6c1aecaf558b8c7a1757d5f2d2ad7 Author: Thomas Gleixner <[email protected]> AuthorDate: Tue, 19 May 2015 00:00:53 +0000 Committer: Ingo Molnar <[email protected]> CommitDate: Wed, 27 May 2015 09:17:39 +0200
perf/x86/intel/cqm: Remove pointless spinlock from state cache 'struct intel_cqm_state' is a strict per CPU cache of the rmid and the usage counter. It can never be modified from a remote CPU. The three functions which modify the content: intel_cqm_event[start|stop|del] (del maps to stop) are called from the perf core with interrupts disabled which is enough protection for the per CPU state values. Signed-off-by: Thomas Gleixner <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Acked-by: Matt Fleming <[email protected]> Cc: Kanaka Juvva <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Vikas Shivappa <[email protected]> Cc: Will Auld <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/kernel/cpu/perf_event_intel_cqm.c | 17 ++++++----------- 1 file changed, 6 insertions(+), 11 deletions(-) diff --git a/arch/x86/kernel/cpu/perf_event_intel_cqm.c b/arch/x86/kernel/cpu/perf_event_intel_cqm.c index 3e9a7fb..63391f8 100644 --- a/arch/x86/kernel/cpu/perf_event_intel_cqm.c +++ b/arch/x86/kernel/cpu/perf_event_intel_cqm.c @@ -17,11 +17,16 @@ static unsigned int cqm_max_rmid = -1; static unsigned int cqm_l3_scale; /* supposedly cacheline size */ struct intel_cqm_state { - raw_spinlock_t lock; u32 rmid; int cnt; }; +/* + * The cached intel_cqm_state is strictly per CPU and can never be + * updated from a remote CPU. Both functions which modify the state + * (intel_cqm_event_start and intel_cqm_event_stop) are called with + * interrupts disabled, which is sufficient for the protection. + */ static DEFINE_PER_CPU(struct intel_cqm_state, cqm_state); /* @@ -963,15 +968,12 @@ static void intel_cqm_event_start(struct perf_event *event, int mode) { struct intel_cqm_state *state = this_cpu_ptr(&cqm_state); u32 rmid = event->hw.cqm_rmid; - unsigned long flags; if (!(event->hw.cqm_state & PERF_HES_STOPPED)) return; event->hw.cqm_state &= ~PERF_HES_STOPPED; - raw_spin_lock_irqsave(&state->lock, flags); - if (state->cnt++) WARN_ON_ONCE(state->rmid != rmid); else @@ -984,21 +986,17 @@ static void intel_cqm_event_start(struct perf_event *event, int mode) * Technology component. */ wrmsr(MSR_IA32_PQR_ASSOC, rmid, 0); - - raw_spin_unlock_irqrestore(&state->lock, flags); } static void intel_cqm_event_stop(struct perf_event *event, int mode) { struct intel_cqm_state *state = this_cpu_ptr(&cqm_state); - unsigned long flags; if (event->hw.cqm_state & PERF_HES_STOPPED) return; event->hw.cqm_state |= PERF_HES_STOPPED; - raw_spin_lock_irqsave(&state->lock, flags); intel_cqm_event_read(event); if (!--state->cnt) { @@ -1013,8 +1011,6 @@ static void intel_cqm_event_stop(struct perf_event *event, int mode) } else { WARN_ON_ONCE(!state->rmid); } - - raw_spin_unlock_irqrestore(&state->lock, flags); } static int intel_cqm_event_add(struct perf_event *event, int mode) @@ -1257,7 +1253,6 @@ static void intel_cqm_cpu_prepare(unsigned int cpu) struct intel_cqm_state *state = &per_cpu(cqm_state, cpu); struct cpuinfo_x86 *c = &cpu_data(cpu); - raw_spin_lock_init(&state->lock); state->rmid = 0; state->cnt = 0; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
