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SubjectRe: [PATCH -tip/perf/core] perf, x86: P4 PMU - Introduce event alias feature

* Cyrill Gorcunov <gorcunov@openvz.org> wrote:

> @@ -102,6 +102,14 @@
> #define P4_CONFIG_HT (1ULL << P4_CONFIG_HT_SHIFT)
>
> /*
> + * If an event has alias it should be marked
> + * with a special bit. (Don't forget to check
> + * P4_PEBS_CONFIG_MASK and related bits on
> + * modification.)
> + */
> +#define P4_CONFIG_ALIASABLE (1 << 9)
> +
> +/*
> * The bits we allow to pass for RAW events
> */
> #define P4_CONFIG_MASK_ESCR \
> @@ -123,6 +131,31 @@
> (p4_config_pack_escr(P4_CONFIG_MASK_ESCR)) | \
> (p4_config_pack_cccr(P4_CONFIG_MASK_CCCR))
>
> +/*
> + * In case of event aliasing we need to preserve some
> + * caller bits otherwise the mapping won't be complete.

Missing comma.

> + */
> +#define P4_CONFIG_EVENT_ALIAS_MASK \
> + (p4_config_pack_escr(P4_CONFIG_MASK_ESCR) | \
> + p4_config_pack_cccr(P4_CCCR_EDGE | \
> + P4_CCCR_THRESHOLD_MASK | \
> + P4_CCCR_COMPLEMENT | \
> + P4_CCCR_COMPARE))
> +
> +#define P4_CONFIG_EVENT_ALIAS_IMMUTABLE_BITS \
> + ((P4_CONFIG_HT) | \
> + p4_config_pack_escr(P4_ESCR_T0_OS | \
> + P4_ESCR_T0_USR | \
> + P4_ESCR_T1_OS | \
> + P4_ESCR_T1_USR) | \
> + p4_config_pack_cccr(P4_CCCR_OVF | \
> + P4_CCCR_CASCADE | \
> + P4_CCCR_FORCE_OVF | \
> + P4_CCCR_THREAD_ANY | \
> + P4_CCCR_OVF_PMI_T0 | \
> + P4_CCCR_OVF_PMI_T1 | \
> + P4_CONFIG_ALIASABLE))
> +
> static inline bool p4_is_event_cascaded(u64 config)
> {
> u32 cccr = p4_config_unpack_cccr(config);
> 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
> @@ -274,7 +274,6 @@ 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;
> @@ -360,12 +359,6 @@ 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
> @@ -570,11 +570,92 @@ static __initconst const u64 p4_hw_cache
> },
> };
>
> +/*
> + * Because of Netburst being quite restricted in now
> + * many same events can run simultaneously, we use

typo(s).

> + * event aliases, ie different events which have the
> + * same functionallity but use non-intersected resources
> + * (ESCR/CCCR/couter registers). This allow us to run
> + * two or more semi-same events together. It is done
> + * transparently to a user space.

typo.

> + *
> + * Never set any cusom internal bits such as P4_CONFIG_HT,
> + * P4_CONFIG_ALIASABLE or bits for P4_PEBS_METRIC, they are
> + * either up-to-dated automatically either not appliable

typo(s).

> + * at all.
> + *
> + * And be really carefull choosing aliases!

typo.

> + */
> +struct p4_event_alias {
> + u64 orig;
> + u64 alter;

what is an 'alter'? alias? alternate?

> +} p4_event_aliases[] = {
> + {
> + /*
> + * Non-halted cycles can be substituted with
> + * non-sleeping cycles (see Intel SDM Vol3b for
> + * details).
> + */
> + .orig =
> + p4_config_pack_escr(P4_ESCR_EVENT(P4_EVENT_GLOBAL_POWER_EVENTS) |
> + P4_ESCR_EMASK_BIT(P4_EVENT_GLOBAL_POWER_EVENTS, RUNNING)),
> + .alter =
> + 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),

That currently we only offer an alias for the generic cycles event is
an important property - yet it's only visible from the code and is
not mentioned in any of the voluminous comments. Good comments are to
the point and focused: what problem is being solved, how is it solved
and what are the limitations of the solution.

> + },
> +};
> +
> +static u64 p4_get_alias_event(u64 config)
> +{
> + u64 config_match;
> + int i;
> +
> + /*
> + * Probably we're lucky and don't have to do
> + * matching over all config bits.
> + */
> + if (!(config & P4_CONFIG_ALIASABLE))
> + return 0;

'all' config bits? There's a single alias mapping in
p4_event_aliases[] right now which makes the comment rather
misleading ...

> +
> + config_match = config & P4_CONFIG_EVENT_ALIAS_MASK;
> +
> + /*
> + * If an event was previously swapped to the alter config
> + * we should swap it back otherwise contnention on registers
> + * will return back.

'alter config' is a new English word apparently. We can invent new
words but is it really warranted here? 'alternate config'? 'config
alias'?

> + */
> + for (i = 0; i < ARRAY_SIZE(p4_event_aliases); i++) {
> + if (config_match == p4_event_aliases[i].orig) {
> + config_match = p4_event_aliases[i].alter;
> + break;
> + } else if (config_match == p4_event_aliases[i].alter) {
> + config_match = p4_event_aliases[i].orig;
> + break;
> + }
> + }

Since this .c file is P4 specific and p4_event_aliases[] is a
file-scope array, is the p4_ prefix even needed?

> +
> + if (i >= ARRAY_SIZE(p4_event_aliases))
> + return 0;
> +
> + return (config_match |
> + (config & P4_CONFIG_EVENT_ALIAS_IMMUTABLE_BITS));

'return' is not a function. Also, please don't break the line
pointlessly.

> +}
> +
> static u64 p4_general_events[PERF_COUNT_HW_MAX] = {
> /* non-halted CPU clocks */
> [PERF_COUNT_HW_CPU_CYCLES] =
> p4_config_pack_escr(P4_ESCR_EVENT(P4_EVENT_GLOBAL_POWER_EVENTS) |
> - P4_ESCR_EMASK_BIT(P4_EVENT_GLOBAL_POWER_EVENTS, RUNNING)),
> + P4_ESCR_EMASK_BIT(P4_EVENT_GLOBAL_POWER_EVENTS, RUNNING)) |
> + P4_CONFIG_ALIASABLE,
>
> /*
> * retired instructions
> @@ -719,31 +800,6 @@ 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();
> @@ -1159,6 +1215,8 @@ static int p4_pmu_schedule_events(struct
> struct p4_event_bind *bind;
> unsigned int i, thread, num;
> int cntr_idx, escr_idx;
> + u64 config_alias;
> + int pass;
>
> bitmap_zero(used_mask, X86_PMC_IDX_MAX);
> bitmap_zero(escr_mask, P4_ESCR_MSR_TABLE_SIZE);
> @@ -1167,6 +1225,17 @@ static int p4_pmu_schedule_events(struct
>
> hwc = &cpuc->event_list[i]->hw;
> thread = p4_ht_thread(cpu);
> + pass = 0;
> +
> +again:
> + /*
> + * Aliases are swappable so we may hit circular
> + * lock if both original config and alias need
> + * resources (MSR registers) which already busy.

typo.

> + */
> + if (pass > 2)
> + goto done;
> +
> bind = p4_config_get_bind(hwc->config);
> escr_idx = p4_get_escr_idx(bind->escr_msr[thread]);
> if (unlikely(escr_idx == -1))
> @@ -1180,8 +1249,17 @@ static int p4_pmu_schedule_events(struct
> }
>
> cntr_idx = p4_next_cntr(thread, used_mask, bind);
> - if (cntr_idx == -1 || test_bit(escr_idx, escr_mask))
> - goto done;
> + if (cntr_idx == -1 || test_bit(escr_idx, escr_mask)) {
> + /*
> + * Probably an event alias is still available.

s/Probably/Possibly?

> + */
> + config_alias = p4_get_alias_event(hwc->config);
> + if (!config_alias)
> + goto done;
> + hwc->config = config_alias;
> + pass++;
> + goto again;
> + }
>
> p4_pmu_swap_config_ts(hwc, cpu);
> if (assign)
> @@ -1218,7 +1296,6 @@ 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
> @@ -200,7 +200,6 @@ 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,
> @@ -372,7 +371,6 @@ static int watchdog_nmi_enable(int cpu)
>
> 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, NULL);

This looks like the right approach otherwise. Peter?

Thanks,

Ingo


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