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

tip-bot for Ingo Molnar
2009-05-18T07:42:55Z

Commit-ID: b68f1d2e7aa21029d73c7d453a8046e95d351740
Gitweb: http://git.kernel.org/tip/b68f1d2e7aa21029d73c7d453a8046e95d351740
Author: Ingo Molnar <mingo@elte.hu>
AuthorDate: Sun, 17 May 2009 19:37:25 +0200
Committer: Ingo Molnar <mingo@elte.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@chello.nl>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.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);
}