Messages in this thread | | | Subject | Re: [PATCH v13 5/8] perf record: Read from overwritable ring buffer | From | "Wangnan (F)" <> | Date | Thu, 7 Jul 2016 12:59:41 +0800 |
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On 2016/7/6 20:34, Jiri Olsa wrote: > On Wed, Jul 06, 2016 at 08:03:28PM +0800, Wangnan (F) wrote: >> >> On 2016/7/6 19:38, Jiri Olsa wrote: >>> On Mon, Jul 04, 2016 at 06:20:06AM +0000, Wang Nan wrote: >>> >>> SNIP >>> >>>> +static void >>>> +record__toggle_overwrite_evsels(struct record *rec, >>>> + enum overwrite_evt_state state) >>>> +{ >>>> + struct perf_evlist *evlist = rec->overwrite_evlist; >>>> + enum overwrite_evt_state old_state = rec->overwrite_evt_state; >>>> + enum action { >>>> + NONE, >>>> + PAUSE, >>>> + RESUME, >>>> + } action = NONE; >>>> + >>>> + switch (old_state) { >>>> + case OVERWRITE_EVT_RUNNING: { >>>> + switch (state) { >>>> + case OVERWRITE_EVT_DATA_PENDING: >>>> + action = PAUSE; >>>> + break; >>>> + case OVERWRITE_EVT_RUNNING: >>>> + case OVERWRITE_EVT_EMPTY: >>>> + default: >>>> + goto state_err; >>>> + } >>>> + break; >>>> + } >>>> + case OVERWRITE_EVT_DATA_PENDING: { >>>> + switch (state) { >>>> + case OVERWRITE_EVT_EMPTY: >>>> + break; >>>> + case OVERWRITE_EVT_RUNNING: >>>> + case OVERWRITE_EVT_DATA_PENDING: >>>> + default: >>>> + goto state_err; >>>> + } >>>> + break; >>>> + } >>>> + case OVERWRITE_EVT_EMPTY: { >>>> + switch (state) { >>>> + case OVERWRITE_EVT_RUNNING: >>>> + action = RESUME; >>>> + break; >>>> + case OVERWRITE_EVT_EMPTY: >>>> + case OVERWRITE_EVT_DATA_PENDING: >>>> + default: >>>> + goto state_err; >>>> + } >>>> + break; >>>> + } >>>> + default: >>>> + WARN_ONCE(1, "Shouldn't get there\n"); >>>> + } >>>> + >>>> + rec->overwrite_evt_state = state; >>>> + >>>> + if (!evlist) >>>> + return; >>> I'd expect this check at the begining >> I think even evlist is NULL the state changing is still required. >> Actually, the state machine is independent with aux evlist. Even >> we without overwritable evsels the state machine is still valid. >> So let the state machine runs unconditionally. > hum, can't see that.. it's state machine to govern overwrite evlist, right? > if there's no overwrite evlist we should keep the current processing
Not as easy as I thought. Look at following code:
>@@ -1006,8 +1122,27 @@ static int __cmd_record(struct record *rec, int argc, const char **argv) > } > > if (trigger_is_hit(&switch_output_trigger)) { >+ /* >+ * If switch_output_trigger is hit, the data in >+ * overwritable ring buffer should have been collected, >+ * so overwrite_evt_state should be set to >+ * OVERWRITE_EVT_EMPTY. >+ * >+ * If SIGUSR2 raise after or during record__mmap_read_all(), >+ * record__mmap_read_all() didn't collect data from >+ * overwritable ring buffer. Read again. >+ */ >+ if (rec->overwrite_evt_state == OVERWRITE_EVT_RUNNING) >+ continue; > trigger_ready(&switch_output_trigger); > >+ /* >+ * Reenable events in overwrite ring buffer after >+ * record__mmap_read_all(): we should have collected >+ * data from it. >+ */ >+ record__toggle_overwrite_evsels(rec, OVERWRITE_EVT_RUNNING); >+ > if (!quiet) > fprintf(stderr, "[ perf record: dump data: Woken up %ld times ]\n", > waking);
Here perf tests whether reading from overwritable ring buffer is required. If SIGUSR2 is received just before the above trigger_is_hit, we should read from overwrite ring buffer again. The OVERWRITE_EVT_RUNNING checker is for this reason.
Now if we stop the state machine, the state is stopped at OVERWRITE_EVT_RUNNING, causes perf loops forever.
We can check rec->overwrite_evlist first, but it is ugly, since I believe the overwritable state is independent to overwrite evlist. So I decide to introduce a new state indicate the overwrite evlist is not ready.
Thank you.
> if it's meant to govern the mmap reading in general > we should at least rename it > jirka
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