Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755805AbZKWIib (ORCPT ); Mon, 23 Nov 2009 03:38:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755561AbZKWIia (ORCPT ); Mon, 23 Nov 2009 03:38:30 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:40443 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752884AbZKWIia (ORCPT ); Mon, 23 Nov 2009 03:38:30 -0500 Subject: Re: [PATCH 03/15] perf: optimize perf_swevent_ctx_event() From: Peter Zijlstra To: Paul Mackerras Cc: Ingo Molnar , linux-kernel@vger.kernel.org In-Reply-To: <1258961500.4531.38.camel@laptop> References: <20091120211942.676891948@chello.nl> <20091120212508.378188589@chello.nl> <19210.8856.446670.786636@cargo.ozlabs.ibm.com> <1258961500.4531.38.camel@laptop> Content-Type: text/plain; charset="UTF-8" Date: Mon, 23 Nov 2009 09:38:32 +0100 Message-ID: <1258965512.4531.113.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4524 Lines: 130 On Mon, 2009-11-23 at 08:31 +0100, Peter Zijlstra wrote: > On Mon, 2009-11-23 at 16:50 +1100, Paul Mackerras wrote: > > Peter Zijlstra writes: > > > > > We can do away with the system_state check if the machine still boots > > > after this patch (seems to be the case). > > > > I have a recollection (possible faulty) that the problem we can get > > into if we don't have this check is that if we take a bad page fault > > in the kernel (e.g. NULL dereference) early in boot before the perf > > cpu context has been initialized, we then get another NULL dereference > > because the pointers in ctx->event_list are NULL, and recurse to > > death. > > > > So that check was possibly more about debugging than correctness. > > Possibly also the x86 do_page_fault() is different enough from the > > powerpc one that the problem can't occur on x86. > > Right, I remembered there was _something_ we added them for, but > couldn't for the live of me remember what. > > Hmm, maybe we can initialize all the recursion variables to 1, that > should avoid us ever entering into the swcounter code until we reset > them. I think the below patch fixed that.. --- commit f29ac756a40d0f1bb07d682ea521e7b666ff06d5 Author: Peter Zijlstra Date: Fri Jun 19 18:27:26 2009 +0200 perf_counter: Optimize perf_swcounter_event() Similar to tracepoints, use an enable variable to reduce overhead when unused. Only look for a counter of a particular event type when we know there is at least one in the system. Signed-off-by: Peter Zijlstra LKML-Reference: Cc: Mike Galbraith Cc: Paul Mackerras Cc: Arnaldo Carvalho de Melo Signed-off-by: Ingo Molnar diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h index 89698d8..e7213e4 100644 --- a/include/linux/perf_counter.h +++ b/include/linux/perf_counter.h @@ -669,7 +669,16 @@ static inline int is_software_counter(struct perf_counter *counter) (counter->attr.type != PERF_TYPE_HW_CACHE); } -extern void perf_swcounter_event(u32, u64, int, struct pt_regs *, u64); +extern atomic_t perf_swcounter_enabled[PERF_COUNT_SW_MAX]; + +extern void __perf_swcounter_event(u32, u64, int, struct pt_regs *, u64); + +static inline void +perf_swcounter_event(u32 event, u64 nr, int nmi, struct pt_regs *regs, u64 addr) +{ + if (atomic_read(&perf_swcounter_enabled[event])) + __perf_swcounter_event(event, nr, nmi, regs, addr); +} extern void __perf_counter_mmap(struct vm_area_struct *vma); diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c index 1a933a2..7515c76 100644 --- a/kernel/perf_counter.c +++ b/kernel/perf_counter.c @@ -3317,8 +3317,8 @@ out: put_cpu_var(perf_cpu_context); } -void -perf_swcounter_event(u32 event, u64 nr, int nmi, struct pt_regs *regs, u64 addr) +void __perf_swcounter_event(u32 event, u64 nr, int nmi, + struct pt_regs *regs, u64 addr) { struct perf_sample_data data = { .regs = regs, @@ -3509,9 +3509,19 @@ static const struct pmu *tp_perf_counter_init(struct perf_counter *counter) } #endif +atomic_t perf_swcounter_enabled[PERF_COUNT_SW_MAX]; + +static void sw_perf_counter_destroy(struct perf_counter *counter) +{ + u64 event = counter->attr.config; + + atomic_dec(&perf_swcounter_enabled[event]); +} + static const struct pmu *sw_perf_counter_init(struct perf_counter *counter) { const struct pmu *pmu = NULL; + u64 event = counter->attr.config; /* * Software counters (currently) can't in general distinguish @@ -3520,7 +3530,7 @@ static const struct pmu *sw_perf_counter_init(struct perf_counter *counter) * to be kernel events, and page faults are never hypervisor * events. */ - switch (counter->attr.config) { + switch (event) { case PERF_COUNT_SW_CPU_CLOCK: pmu = &perf_ops_cpu_clock; @@ -3541,6 +3551,8 @@ static const struct pmu *sw_perf_counter_init(struct perf_counter *counter) case PERF_COUNT_SW_PAGE_FAULTS_MAJ: case PERF_COUNT_SW_CONTEXT_SWITCHES: case PERF_COUNT_SW_CPU_MIGRATIONS: + atomic_inc(&perf_swcounter_enabled[event]); + counter->destroy = sw_perf_counter_destroy; pmu = &perf_ops_generic; break; } -- 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/