From b0e878759452314676fbdd71df4ac67e7d08de5d Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 28 Aug 2015 14:06:07 +0200 Subject: [PATCH] perf/abi: Document some more aspects of the perf ABI Signed-off-by: Peter Zijlstra (Intel) Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- include/linux/perf_event.h | 117 +++++++++++++++++++++++++++++++------ 1 file changed, 98 insertions(+), 19 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 092a0e8a479a..d61ee4459eee 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -140,27 +140,60 @@ struct hw_perf_event { }; #endif }; + /* + * If the event is a per task event, this will point to the task in + * question. See the comment in perf_event_alloc(). + */ struct task_struct *target; - int state; - local64_t prev_count; - u64 sample_period; - u64 last_period; - local64_t period_left; - u64 interrupts_seq; - u64 interrupts; - - u64 freq_time_stamp; - u64 freq_count_stamp; -#endif -}; /* - * hw_perf_event::state flags + * hw_perf_event::state flags; used to track the PERF_EF_* state. */ #define PERF_HES_STOPPED 0x01 /* the counter is stopped */ #define PERF_HES_UPTODATE 0x02 /* event->count up-to-date */ #define PERF_HES_ARCH 0x04 + int state; + + /* + * The last observed hardware counter value, updated with a + * local64_cmpxchg() such that pmu::read() can be called nested. + */ + local64_t prev_count; + + /* + * The period to start the next sample with. + */ + u64 sample_period; + + /* + * The period we started this sample with. + */ + u64 last_period; + + /* + * However much is left of the current period; note that this is + * a full 64bit value and allows for generation of periods longer + * than hardware might allow. + */ + local64_t period_left; + + /* + * State for throttling the event, see __perf_event_overflow() and + * perf_adjust_freq_unthr_context(). + */ + u64 interrupts_seq; + u64 interrupts; + + /* + * State for freq target events, see __perf_event_overflow() and + * perf_adjust_freq_unthr_context(). + */ + u64 freq_time_stamp; + u64 freq_count_stamp; +#endif +}; + struct perf_event; /* @@ -210,7 +243,19 @@ struct pmu { /* * Try and initialize the event for this PMU. - * Should return -ENOENT when the @event doesn't match this PMU. + * + * Returns: + * -ENOENT -- @event is not for this PMU + * + * -ENODEV -- @event is for this PMU but PMU not present + * -EBUSY -- @event is for this PMU but PMU temporarily unavailable + * -EINVAL -- @event is for this PMU but @event is not valid + * -EOPNOTSUPP -- @event is for this PMU, @event is valid, but not supported + * -EACCESS -- @event is for this PMU, @event is valid, but no privilidges + * + * 0 -- @event is for this PMU and valid + * + * Other error return values are allowed. */ int (*event_init) (struct perf_event *event); @@ -221,27 +266,61 @@ struct pmu { void (*event_mapped) (struct perf_event *event); /*optional*/ void (*event_unmapped) (struct perf_event *event); /*optional*/ + /* + * Flags for ->add()/->del()/ ->start()/->stop(). There are + * matching hw_perf_event::state flags. + */ #define PERF_EF_START 0x01 /* start the counter when adding */ #define PERF_EF_RELOAD 0x02 /* reload the counter when starting */ #define PERF_EF_UPDATE 0x04 /* update the counter when stopping */ /* - * Adds/Removes a counter to/from the PMU, can be done inside - * a transaction, see the ->*_txn() methods. + * Adds/Removes a counter to/from the PMU, can be done inside a + * transaction, see the ->*_txn() methods. + * + * The add/del callbacks will reserve all hardware resources required + * to service the event, this includes any counter constraint + * scheduling etc. + * + * Called with IRQs disabled and the PMU disabled on the CPU the event + * is on. + * + * ->add() called without PERF_EF_START should result in the same state + * as ->add() followed by ->stop(). + * + * ->del() must always PERF_EF_UPDATE stop an event. If it calls + * ->stop() that must deal with already being stopped without + * PERF_EF_UPDATE. */ int (*add) (struct perf_event *event, int flags); void (*del) (struct perf_event *event, int flags); /* - * Starts/Stops a counter present on the PMU. The PMI handler - * should stop the counter when perf_event_overflow() returns - * !0. ->start() will be used to continue. + * Starts/Stops a counter present on the PMU. + * + * The PMI handler should stop the counter when perf_event_overflow() + * returns !0. ->start() will be used to continue. + * + * Also used to change the sample period. + * + * Called with IRQs disabled and the PMU disabled on the CPU the event + * is on -- will be called from NMI context with the PMU generates + * NMIs. + * + * ->stop() with PERF_EF_UPDATE will read the counter and update + * period/count values like ->read() would. + * + * ->start() with PERF_EF_RELOAD will reprogram the the counter + * value, must be preceded by a ->stop() with PERF_EF_UPDATE. */ void (*start) (struct perf_event *event, int flags); void (*stop) (struct perf_event *event, int flags); /* * Updates the counter value of the event. + * + * For sampling capable PMUs this will also update the software period + * hw_perf_event::period_left field. */ void (*read) (struct perf_event *event);