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perf_counter, x86: Fix/improve apic fallback
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Johannes Stezenbach reported that his Pentium-M based
laptop does not have the local APIC enabled by default,
and hence perfcounters do not get initialized.

Add a fallback for this case: allow non-sampled counters
and return with an error on sampled counters. This allows
'perf stat' to work out of box - and allows 'perf top'
and 'perf record' to fall back on a hrtimer based sampling
method.

( Passing 'lapic' on the boot line will allow hardware
  sampling to occur - but if the APIC is disabled
  permanently by the hardware then this fallback still
  allows more systems to use perfcounters. )

Also decouple perfcounter support from X86_LOCAL_APIC.

-v2: fix typo breaking counters on all other systems ...

Reported-by: Johannes Stezenbach <js@sig21.net>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Ingo Molnar committed Aug 12, 2009
1 parent 0a5ac84 commit 04da8a4
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Showing 2 changed files with 31 additions and 5 deletions.
2 changes: 1 addition & 1 deletion arch/x86/Kconfig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@ config X86
select HAVE_UNSTABLE_SCHED_CLOCK
select HAVE_IDE
select HAVE_OPROFILE
select HAVE_PERF_COUNTERS if (!M386 && !M486)
select HAVE_IOREMAP_PROT
select HAVE_KPROBES
select ARCH_WANT_OPTIONAL_GPIOLIB
Expand Down Expand Up @@ -742,7 +743,6 @@ config X86_UP_IOAPIC
config X86_LOCAL_APIC
def_bool y
depends on X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC
select HAVE_PERF_COUNTERS if (!M386 && !M486)

config X86_IO_APIC
def_bool y
Expand Down
34 changes: 30 additions & 4 deletions arch/x86/kernel/cpu/perf_counter.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,7 @@ struct x86_pmu {
int num_counters_fixed;
int counter_bits;
u64 counter_mask;
int apic;
u64 max_period;
u64 intel_ctrl;
};
Expand Down Expand Up @@ -613,6 +614,7 @@ static DEFINE_MUTEX(pmc_reserve_mutex);

static bool reserve_pmc_hardware(void)
{
#ifdef CONFIG_X86_LOCAL_APIC
int i;

if (nmi_watchdog == NMI_LOCAL_APIC)
Expand All @@ -627,9 +629,11 @@ static bool reserve_pmc_hardware(void)
if (!reserve_evntsel_nmi(x86_pmu.eventsel + i))
goto eventsel_fail;
}
#endif

return true;

#ifdef CONFIG_X86_LOCAL_APIC
eventsel_fail:
for (i--; i >= 0; i--)
release_evntsel_nmi(x86_pmu.eventsel + i);
Expand All @@ -644,10 +648,12 @@ static bool reserve_pmc_hardware(void)
enable_lapic_nmi_watchdog();

return false;
#endif
}

static void release_pmc_hardware(void)
{
#ifdef CONFIG_X86_LOCAL_APIC
int i;

for (i = 0; i < x86_pmu.num_counters; i++) {
Expand All @@ -657,6 +663,7 @@ static void release_pmc_hardware(void)

if (nmi_watchdog == NMI_LOCAL_APIC)
enable_lapic_nmi_watchdog();
#endif
}

static void hw_perf_counter_destroy(struct perf_counter *counter)
Expand Down Expand Up @@ -748,6 +755,15 @@ static int __hw_perf_counter_init(struct perf_counter *counter)
hwc->sample_period = x86_pmu.max_period;
hwc->last_period = hwc->sample_period;
atomic64_set(&hwc->period_left, hwc->sample_period);
} else {
/*
* If we have a PMU initialized but no APIC
* interrupts, we cannot sample hardware
* counters (user-space has to fall back and
* sample via a hrtimer based software counter):
*/
if (!x86_pmu.apic)
return -EOPNOTSUPP;
}

counter->destroy = hw_perf_counter_destroy;
Expand Down Expand Up @@ -1449,18 +1465,22 @@ void smp_perf_pending_interrupt(struct pt_regs *regs)

void set_perf_counter_pending(void)
{
#ifdef CONFIG_X86_LOCAL_APIC
apic->send_IPI_self(LOCAL_PENDING_VECTOR);
#endif
}

void perf_counters_lapic_init(void)
{
if (!x86_pmu_initialized())
#ifdef CONFIG_X86_LOCAL_APIC
if (!x86_pmu.apic || !x86_pmu_initialized())
return;

/*
* Always use NMI for PMU
*/
apic_write(APIC_LVTPC, APIC_DM_NMI);
#endif
}

static int __kprobes
Expand All @@ -1484,7 +1504,9 @@ perf_counter_nmi_handler(struct notifier_block *self,

regs = args->regs;

#ifdef CONFIG_X86_LOCAL_APIC
apic_write(APIC_LVTPC, APIC_DM_NMI);
#endif
/*
* Can't rely on the handled return value to say it was our NMI, two
* counters could trigger 'simultaneously' raising two back-to-back NMIs.
Expand Down Expand Up @@ -1515,6 +1537,7 @@ static struct x86_pmu p6_pmu = {
.event_map = p6_pmu_event_map,
.raw_event = p6_pmu_raw_event,
.max_events = ARRAY_SIZE(p6_perfmon_event_map),
.apic = 1,
.max_period = (1ULL << 31) - 1,
.version = 0,
.num_counters = 2,
Expand All @@ -1541,6 +1564,7 @@ static struct x86_pmu intel_pmu = {
.event_map = intel_pmu_event_map,
.raw_event = intel_pmu_raw_event,
.max_events = ARRAY_SIZE(intel_perfmon_event_map),
.apic = 1,
/*
* Intel PMCs cannot be accessed sanely above 32 bit width,
* so we install an artificial 1<<31 period regardless of
Expand All @@ -1564,6 +1588,7 @@ static struct x86_pmu amd_pmu = {
.num_counters = 4,
.counter_bits = 48,
.counter_mask = (1ULL << 48) - 1,
.apic = 1,
/* use highest bit to detect overflow */
.max_period = (1ULL << 47) - 1,
};
Expand All @@ -1589,13 +1614,14 @@ static int p6_pmu_init(void)
return -ENODEV;
}

x86_pmu = p6_pmu;

if (!cpu_has_apic) {
pr_info("no APIC, boot with the \"lapic\" boot parameter to force-enable it.\n");
return -ENODEV;
pr_info("no hardware sampling interrupt available.\n");
x86_pmu.apic = 0;
}

x86_pmu = p6_pmu;

return 0;
}

Expand Down

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