On 26.06.2020 13:06, Alexey Budankov wrote: > > On 26.06.2020 12:37, Jiri Olsa wrote: >> On Thu, Jun 25, 2020 at 10:32:29PM +0300, Alexey Budankov wrote: >>> >>> On 25.06.2020 20:14, Jiri Olsa wrote: >>>> On Wed, Jun 24, 2020 at 08:19:32PM +0300, Alexey Budankov wrote: >>>>> >>>>> On 17.06.2020 11:35, Alexey Budankov wrote: >>>>>> >>>>>> Skip fds with zeroed revents field from count and avoid fds moving >>>>>> at fdarray__filter() call so fds indices returned by fdarray__add() >>>>>> call stay the same and can be used for direct access and processing >>>>>> of fd revents status field at entries array of struct fdarray object. >>>>>> >>>>>> Signed-off-by: Alexey Budankov <[email protected]> >>>>>> --- >>>>>> tools/lib/api/fd/array.c | 11 +++++------ >>>>>> tools/perf/tests/fdarray.c | 20 ++------------------ >>>>>> 2 files changed, 7 insertions(+), 24 deletions(-) >>>>>> >>>>>> diff --git a/tools/lib/api/fd/array.c b/tools/lib/api/fd/array.c >>>>>> index 58d44d5eee31..97843a837370 100644 >>>>>> --- a/tools/lib/api/fd/array.c >>>>>> +++ b/tools/lib/api/fd/array.c >>>>>> @@ -93,22 +93,21 @@ int fdarray__filter(struct fdarray *fda, short >>>>>> revents, >>>>>> return 0; >>>>>> >>>>>> for (fd = 0; fd < fda->nr; ++fd) { >>>>>> + if (!fda->entries[fd].revents) >>>>>> + continue; >>>>>> + >>>>> >>>>> So it looks like this condition also filters out non signaling events >>>>> fds, not only >>>>> control and others fds, and this should be somehow avoided so such event >>>>> related fds >>>>> would be counted. Several options have been proposed so far: >>>>> >>>>> 1) Explicit typing of fds via API extension and filtering based on the >>>>> types: >>>>> a) with separate fdarray__add_stat() call >>>>> b) with type arg of existing fdarray__add() call >>>>> c) various memory management design is possible >>>>> >>>>> 2) Playing tricks with fd positions inside entries and assumptions on >>>>> fdarray API calls ordering >>>>> - looks more like a hack than a designed solution >>>>> >>>>> 3) Rewrite of fdarray class to allocate separate object for every added >>>>> fds >>>>> - can be replaced with nonscrewing of fds by __filter() >>>>> >>>>> 4) Distinct between fds types at fdarray__filter() using .revents == 0 >>>>> condition >>>>> - seems to have corner cases and thus not applicable >>>>> >>>>> 5) Extension of fdarray__poll(, *arg_ptr, arg_size) with arg of fds array >>>>> to atomically poll >>>>> on fdarray_add()-ed fds and external arg fds and then external arg fds >>>>> processing >>>>> >>>>> 6) Rewrite of fdarray class on epoll() call basis >>>>> - introduces new scalability restrictions for Perf tool >>>> >>>> hum, how many fds for polling do you expect in your workloads? >>> >>> Currently it is several hundreds so default of 1K is easily hit and >>> "Profile a Large Number of PMU Events on Multi-Core Systems" section [1] >>> recommends: >>> >>> soft nofile 65535 >>> hard nofile 65535 >> >> I'm confused, are you talking about file descriptors limit now? >> this wont be affected by epoll change.. what do I miss? > > Currently there is already uname -n limit on the amount of open file > descriptors > and Perf tool process is affected by that limit. > > Moving to epoll() will impose one more max_user_watches limit and that can > additionally > confine Perf applicability even though default value on some machines > currently > is high enough.
Prior making v9 I would prefer to agree on some design to be implemented in order to avoid guessing and redundant reiterating. Options that I see as good balanced ones are 1) or 5), + non screwing of fds to fix staleness of pos(=fdarray__add()). Are there any thoughts so far? ~Aleksei
