linux-kernel - [tip:perfcounters/core] perf_counter, x86: speed up the scheduling fast-path

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Date:	Mon, 18 May 2009 07:40:48 GMT
From:	tip-bot for Ingo Molnar <mingo@...e.hu>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, acme@...hat.com, paulus@...ba.org,
	hpa@...or.com, mingo@...hat.com, a.p.zijlstra@...llo.nl,
	mtosatti@...hat.com, vatsa@...ibm.com, tglx@...utronix.de,
	cjashfor@...ux.vnet.ibm.com, mingo@...e.hu
Subject: [tip:perfcounters/core] perf_counter, x86: speed up the scheduling fast-path

Commit-ID:  b68f1d2e7aa21029d73c7d453a8046e95d351740
Gitweb:     http://git.kernel.org/tip/b68f1d2e7aa21029d73c7d453a8046e95d351740
Author:     Ingo Molnar <mingo@...e.hu>
AuthorDate: Sun, 17 May 2009 19:37:25 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Mon, 18 May 2009 09:37:09 +0200

perf_counter, x86: speed up the scheduling fast-path

We have to set up the LVT entry only at counter init time, not at
every switch-in time.

There's friction between NMI and non-NMI use here - we'll probably
remove the per counter configurability of it - but until then, dont
slow down things ...

[ Impact: micro-optimization ]

Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Srivatsa Vaddagiri <vatsa@...ibm.com>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Corey Ashford <cjashfor@...ux.vnet.ibm.com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Marcelo Tosatti <mtosatti@...hat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 arch/x86/kernel/cpu/perf_counter.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 5bfd30a..c109819 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -285,6 +285,7 @@ static int __hw_perf_counter_init(struct perf_counter *counter)
 			return -EACCES;
 		hwc->nmi = 1;
 	}
+	perf_counters_lapic_init(hwc->nmi);
 
 	if (!hwc->irq_period)
 		hwc->irq_period = x86_pmu.max_period;
@@ -603,8 +604,6 @@ try_generic:
 		hwc->counter_base = x86_pmu.perfctr;
 	}
 
-	perf_counters_lapic_init(hwc->nmi);
-
 	x86_pmu.disable(hwc, idx);
 
 	cpuc->counters[idx] = counter;
@@ -1054,7 +1053,7 @@ void __init init_hw_perf_counters(void)
 
 	pr_info("... counter mask:    %016Lx\n", perf_counter_mask);
 
-	perf_counters_lapic_init(0);
+	perf_counters_lapic_init(1);
 	register_die_notifier(&perf_counter_nmi_notifier);
 }
 
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