From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752952AbbE0KEE (ORCPT ); Wed, 27 May 2015 06:04:04 -0400 Received: from terminus.zytor.com ([198.137.202.10]:33446 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752931AbbE0KEA (ORCPT ); Wed, 27 May 2015 06:04:00 -0400 Date: Wed, 27 May 2015 03:03:31 -0700 From: tip-bot for Thomas Gleixner Message-ID: Cc: matt.fleming@intel.com, kanaka.d.juvva@intel.com, tglx@linutronix.de, peterz@infradead.org, linux-kernel@vger.kernel.org, hpa@zytor.com, will.auld@intel.com, vikas.shivappa@linux.intel.com, mingo@kernel.org, torvalds@linux-foundation.org Reply-To: matt.fleming@intel.com, kanaka.d.juvva@intel.com, tglx@linutronix.de, peterz@infradead.org, linux-kernel@vger.kernel.org, hpa@zytor.com, will.auld@intel.com, vikas.shivappa@linux.intel.com, mingo@kernel.org, torvalds@linux-foundation.org In-Reply-To: <20150518235150.001006529@linutronix.de> References: <20150518235150.001006529@linutronix.de> To: linux-tip-commits@vger.kernel.org Subject: [tip:perf/core] perf/x86/intel/cqm: Remove pointless spinlock from state cache Git-Commit-ID: 9e7eaac95af6c1aecaf558b8c7a1757d5f2d2ad7 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 9e7eaac95af6c1aecaf558b8c7a1757d5f2d2ad7 Gitweb: http://git.kernel.org/tip/9e7eaac95af6c1aecaf558b8c7a1757d5f2d2ad7 Author: Thomas Gleixner AuthorDate: Tue, 19 May 2015 00:00:53 +0000 Committer: Ingo Molnar 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 Signed-off-by: Peter Zijlstra (Intel) Acked-by: Matt Fleming Cc: Kanaka Juvva Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Vikas Shivappa Cc: Will Auld Link: http://lkml.kernel.org/r/20150518235150.001006529@linutronix.de Signed-off-by: Ingo Molnar --- 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;