Re: [PATCH v2 10/15] perf record: manage thread specific data array

Alexei Budankov
2020-10-26T08:39:27Z

On 24.10.2020 18:44, Jiri Olsa wrote:
> On Wed, Oct 21, 2020 at 07:04:26PM +0300, Alexey Budankov wrote:
>>
>> Provide allocation, initialization, finalization and releasing of
>> thread specific objects at thread specific data array. Allocate
>> thread specific object for every data buffer making one-to-one
>> relation between data buffer and a thread processing the buffer.
>> Deliver event fd related signals to thread's pollfd object.
>> Deliver thread control commands to ctlfd_pos fd of thread 1+.
>> Deliver tool external control commands via ctlfd_pos fd of thread 0.
>>
>> Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
>> ---
>> tools/perf/builtin-record.c | 101 ++++++++++++++++++++++++++++++++++--
>> 1 file changed, 98 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>> index 8e512096a060..89cb8e913fb3 100644
>> --- a/tools/perf/builtin-record.c
>> +++ b/tools/perf/builtin-record.c
>> @@ -884,6 +884,94 @@ static int record__kcore_copy(struct machine *machine, struct perf_data *data)
>> return kcore_copy(from_dir, kcore_dir);
>> }
>>
>> +static int record__alloc_thread_data(struct record *rec, struct mmap *mmaps, int nr_mmaps,
>> + struct fdarray *evlist_pollfd, int ctlfd_pos)
>> +{
>> + int i, j, k, nr_thread_data;
>> + struct thread_data *thread_data;
>> +
>> + rec->nr_thread_data = nr_thread_data = nr_mmaps;
>> + rec->thread_data = thread_data = zalloc(rec->nr_thread_data * sizeof(*(rec->thread_data)));
>> + if (!thread_data) {
>> + pr_err("Failed to allocate thread data\n");
>> + return -ENOMEM;
>> + }
>> +
>> + for (i = 0; i < nr_thread_data; i++) {
>> + short revents;
>> + int pos, fd;
>> +
>> + thread_data[i].tid = -1;
>> +
>> + if (pipe(thread_data[i].comm.msg) ||
>> + pipe(thread_data[i].comm.ack)) {
>> + pr_err("Failed to create thread comm pipes, errno %d\n", errno);
>> + return -ENOMEM;
>> + }
>
> the original code was using state flag and pthread_cond,
> which I think is more readable
>
> https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/commit/?h=perf/record_threads&id=a7da527ff8be69572c6d17525c03c6fe394503c8
> https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/commit/?h=perf/record_threads&id=eb85ce4da64a885fdb6c77cfc5bd71312fe02e2a

Yes, right, but messaging scales better and that critical section
to just increment global counter in memory looked as over complication.

>
>> +
>> + thread_data[i].maps = &mmaps[i];
>> + thread_data[i].nr_mmaps = 1;
>> +
>> + thread_data[i].rec = rec;
>> +
>> + fdarray__init(&(thread_data[i].pollfd), 64);
>> +
>> + for (j = 0; j < thread_data[i].nr_mmaps; j++) {
>> + struct mmap *map = &(thread_data[i].maps[j]);
>> +
>> + for (k = 0; k < evlist_pollfd->nr; k++) {
>> + if (evlist_pollfd->priv[k].ptr != map)
>> + continue;
>> +
>> + fd = evlist_pollfd->entries[k].fd;
>> + revents = evlist_pollfd->entries[k].events;
>> + pos = fdarray__add(&(thread_data[i].pollfd),
>> + fd, revents | POLLERR | POLLHUP,
>> + fdarray_flag__default);
>> + if (pos >= 0)
>> + thread_data[i].pollfd.priv[pos].ptr = map;
>> + else
>> + return -ENOMEM;
>
> I added function for that:
> https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/commit/?h=perf/record_threads&id=8aa6e68a7471b9d25af1a9eebfa9321433366a17

Ok, but it is not clone operation it is more like ordinary adding of
fd into another pollfd object. It could be wrapped into a function
e.g. fdarray__dup(pollfd_dst, fd_src, fd_revents)

Alexei