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Message-ID: <a1fd0e15-026f-6f84-ef82-9c01b7d9d48e@linux.intel.com>
Date: Thu, 2 Apr 2020 18:20:05 +0300
From: Alexey Budankov <alexey.budankov@...ux.intel.com>
To: Jiri Olsa <jolsa@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>,
Namhyung Kim <namhyung@...nel.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Andi Kleen <ak@...ux.intel.com>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/8] perf evlist: implement control command handling
functions
On 02.04.2020 17:17, Jiri Olsa wrote:
> On Fri, Mar 27, 2020 at 11:46:43AM +0300, Alexey Budankov wrote:
>
> SNIP
>
>> +
>> +int perf_evlist__ctlfd_process(struct evlist *evlist, enum evlist_ctl_cmd *cmd)
>> +{
>> + int err = 0;
>> + int ctlfd_pos = evlist->ctl_fd_pos;
>> + struct pollfd *entries = evlist->core.pollfd.entries;
>> +
>> + if (!entries[ctlfd_pos].revents)
>> + return 0;
>> +
>> + if (entries[ctlfd_pos].revents & POLLIN) {
>> + err = perf_evlist__ctlfd_recv(evlist, cmd);
>> + if (err > 0) {
>> + switch (*cmd) {
>> + case CTL_CMD_RESUME:
>> + evlist__enable(evlist);
>> + break;
>> + case CTL_CMD_PAUSE:
>> + evlist__disable(evlist);
>> + break;
>
> would CTL_CMD_ENABLE, CTL_CMD_DISABLE be better fit in here?
Makes sense. Let's have it named like the corresponding ioctls, for clarity.
>
> especialy because we have the 'pause' ioctl for sampling,
> which I was thinking initialy you are using for record,
>
> and it's still might be better fit for sampling than disable, no?
PAUSE_OUTPUT ioctl doesn't stop NMIs but it should be avoided
in order not to affect workload execution during paused intervals.
PERF_EVENT_IOC_PAUSE_OUTPUT (since Linux 4.7)
This allows pausing and resuming the event's ring-buffer. A
paused ring-buffer does not prevent generation of samples, but
simply discards them. The discarded samples are considered
lost, and cause a PERF_RECORD_LOST sample to be generated when
possible. An overflow signal may still be triggered by the
discarded sample even though the ring-buffer remains empty.
The argument is an unsigned 32-bit integer. A nonzero value
pauses the ring-buffer, while a zero value resumes the ring-
buffer.
~Alexey
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