Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755254AbbESAAu (ORCPT ); Mon, 18 May 2015 20:00:50 -0400 Received: from www.linutronix.de ([62.245.132.108]:51762 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755030AbbESAAn (ORCPT ); Mon, 18 May 2015 20:00:43 -0400 Message-Id: <20150518235150.001006529@linutronix.de> User-Agent: quilt/0.63-1 Date: Tue, 19 May 2015 00:00:53 -0000 From: Thomas Gleixner To: LKML Cc: Peter Zijlstra , Vikas Shivappa , x86@kernel.org, Matt Fleming , Will Auld , Kanaka Juvva Subject: [patch 3/6] x86, perf, cqm: Remove pointless spinlock from state cache References: <20150518234114.574556332@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Disposition: inline; filename=x86-perf-cqm-remove-pointless-spinlock.patch X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001,URIBL_BLOCKED=0.001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2975 Lines: 96 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 3 functions which modify the content: start, stop and 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 --- arch/x86/kernel/cpu/perf_event_intel_cqm.c | 17 ++++++----------- 1 file changed, 6 insertions(+), 11 deletions(-) Index: linux/arch/x86/kernel/cpu/perf_event_intel_cqm.c =================================================================== --- linux.orig/arch/x86/kernel/cpu/perf_event_intel_cqm.c +++ linux/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 { 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 * 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 } 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(unsign 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 majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/