Messages in this thread Patch in this message | | | Date | Tue, 5 Jul 2011 16:14:21 +0400 | From | Cyrill Gorcunov <> | Subject | Re: [PATCH -tip, final] perf, x86: Add hw_watchdog_set_attr() in a sake of nmi-watchdog on P4 |
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On Tue, Jul 05, 2011 at 03:49:44PM +0400, Cyrill Gorcunov wrote: > On Tue, Jul 05, 2011 at 01:44:37PM +0200, Ingo Molnar wrote: > ... > > > > What i am missing is that you have not pointed out the *core problem* > > you are fixing and it's not obvious from the changelog either! > > OK, seems I put there some tech details while human readable changelog > was needed. Will fix that, thanks! > > Cyrill
Ingo, what about this one?
Cyrill --- perf, x86: P4 PMU - Add hw_watchdog_set_attr helper to simulate cpu-cycles counting in nmi-watchdog
Because of constraints existed in Netburst PMU counting cpu cycles is allowed for one consumer only.
If the kernel is booted up with nmi-watchdog enabled the watchdog become a consumer of such event and there is no more room left for "perf top" and friends (ie any attempts to count cpu cycles simultaneously with nmi-watchdog doomed to fail).
The patch tries to improve situation a bit -- an event counting non-sleeping cpu clocks is added and assigned to nmi-watchdog only, leaving the former PERF_COUNT_HW_CPU_CYCLES event free, so say "perf top" now can run simultaneously with nmi-watchdog.
Note that there is a disadvantage as well -- MSR_P4_CRU_ESCR2 and MSR_P4_CRU_ESCR3 now always occupied by watchdog so if some application needs this ESCRs the nmi-watchdog should be turned off first, otherwise access to these registers will be never granted.
v2: Add a comment about non-sleeping clockticks spotted by Ingo Molnar. v3: Peter Zijlstra and Stephane Eranian pointed out that making new event global visible (up to userspace) will bring problems supporting this ABI in future. So now this event is x86 specific and hidden from userspace. v4: Stephane proposed to use __weak arch specific callback instead of new hidden generic event.
Tested-and-reviewed-by: Don Zickus <dzickus@redhat.com> Tested-and-reviewed-by: Stephane Eranian <eranian@google.com> Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org> CC: Ingo Molnar <mingo@redhat.com> CC: Lin Ming <ming.m.lin@intel.com> CC: Peter Zijlstra <a.p.zijlstra@chello.nl> CC: Arnaldo Carvalho de Melo <acme@redhat.com> CC: Frederic Weisbecker <fweisbec@gmail.com> --- arch/x86/kernel/cpu/perf_event.c | 7 +++++++ arch/x86/kernel/cpu/perf_event_p4.c | 26 ++++++++++++++++++++++++++ kernel/watchdog.c | 6 +++++- 3 files changed, 38 insertions(+), 1 deletion(-)
Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event.c =================================================================== --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event.c +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event.c @@ -233,6 +233,7 @@ struct x86_pmu { void (*enable_all)(int added); void (*enable)(struct perf_event *); void (*disable)(struct perf_event *); + void (*hw_watchdog_set_attr)(struct perf_event_attr *attr); int (*hw_config)(struct perf_event *event); int (*schedule_events)(struct cpu_hw_events *cpuc, int n, int *assign); unsigned eventsel; @@ -315,6 +316,12 @@ static u64 __read_mostly hw_cache_extra_ [PERF_COUNT_HW_CACHE_OP_MAX] [PERF_COUNT_HW_CACHE_RESULT_MAX]; +void hw_nmi_watchdog_set_attr(struct perf_event_attr *wd_attr) +{ + if (x86_pmu.hw_watchdog_set_attr) + x86_pmu.hw_watchdog_set_attr(wd_attr); +} + /* * Propagate event elapsed time into the generic event. * Can only be executed on the CPU where the event is active. Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c =================================================================== --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c @@ -705,6 +705,31 @@ static int p4_validate_raw_event(struct return 0; } +static void p4_hw_watchdog_set_attr(struct perf_event_attr *wd_attr) +{ + /* + * Watchdog ticks are special on Netburst, we use + * that named "non-sleeping" ticks as recommended + * by Intel SDM Vol3b. + */ + WARN_ON_ONCE(wd_attr->type != PERF_TYPE_HARDWARE || + wd_attr->config != PERF_COUNT_HW_CPU_CYCLES); + + wd_attr->type = PERF_TYPE_RAW; + wd_attr->config = + p4_config_pack_escr(P4_ESCR_EVENT(P4_EVENT_EXECUTION_EVENT) | + P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, NBOGUS0) | + P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, NBOGUS1) | + P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, NBOGUS2) | + P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, NBOGUS3) | + P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, BOGUS0) | + P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, BOGUS1) | + P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, BOGUS2) | + P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, BOGUS3)) | + p4_config_pack_cccr(P4_CCCR_THRESHOLD(15) | P4_CCCR_COMPLEMENT | + P4_CCCR_COMPARE); +} + static int p4_hw_config(struct perf_event *event) { int cpu = get_cpu(); @@ -1179,6 +1204,7 @@ static __initconst const struct x86_pmu .cntval_bits = ARCH_P4_CNTRVAL_BITS, .cntval_mask = ARCH_P4_CNTRVAL_MASK, .max_period = (1ULL << (ARCH_P4_CNTRVAL_BITS - 1)) - 1, + .hw_watchdog_set_attr = p4_hw_watchdog_set_attr, .hw_config = p4_hw_config, .schedule_events = p4_pmu_schedule_events, /* Index: linux-2.6.git/kernel/watchdog.c =================================================================== --- linux-2.6.git.orig/kernel/watchdog.c +++ linux-2.6.git/kernel/watchdog.c @@ -200,6 +200,8 @@ static int is_softlockup(unsigned long t } #ifdef CONFIG_HARDLOCKUP_DETECTOR +void __weak hw_nmi_watchdog_set_attr(struct perf_event_attr *wd_attr) { } + static struct perf_event_attr wd_hw_attr = { .type = PERF_TYPE_HARDWARE, .config = PERF_COUNT_HW_CPU_CYCLES, @@ -368,9 +370,11 @@ static int watchdog_nmi_enable(int cpu) if (event != NULL) goto out_enable; - /* Try to register using hardware perf events */ wd_attr = &wd_hw_attr; wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh); + hw_nmi_watchdog_set_attr(wd_attr); + + /* Try to register using hardware perf events */ event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback); if (!IS_ERR(event)) { printk(KERN_INFO "NMI watchdog enabled, takes one hw-pmu counter.\n");
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