Re: [PATCH] perf data: Increase RLIMIT_NOFILE limit when open too many files in perf_data__create_dir()

[Yang Jihong <yangjihong1@huawei.com>]

Hello,

On 2023/10/20 13:59, Namhyung Kim wrote:
> Hello,
> 
> On Fri, Oct 13, 2023 at 1:01 AM Yang Jihong <yangjihong1@huawei.com> wrote:
>>
>> If using parallel threads to collect data, perf record needs at least 6 fds
>> per CPU. (one for sys_perf_event_open, four for pipe msg and ack of the
>> pipe, see record__thread_data_open_pipes(), and one for open perf.data.XXX)
> 
> Yep, probably one more for the dummy event.
> 
>> For an environment with more than 100 cores, if perf record uses both
>> `-a` and `--threads` options, it is easy to exceed the upper limit of the
>> file descriptor number, when we run out of them try to increase the limits.
>>
>> Before:
>>    $ ulimit -n
>>    1024
>>    $ lscpu | grep 'On-line CPU(s)'
>>    On-line CPU(s) list:                0-159
>>    $ perf record --threads -a sleep 1
>>    Failed to create data directory: Too many open files
>>
>> After:
>>    $ ulimit -n
>>    1024
>>    $ lscpu | grep 'On-line CPU(s)'
>>    On-line CPU(s) list:                0-159
>>    $ perf record --threads -a sleep 1
>>    [ perf record: Woken up 1 times to write data ]
>>    [ perf record: Captured and wrote 0.394 MB perf.data (1576 samples) ]
>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
>> ---
>>   tools/perf/util/data.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
>> index fc16299c915f..098f9e3bb2e7 100644
>> --- a/tools/perf/util/data.c
>> +++ b/tools/perf/util/data.c
>> @@ -17,6 +17,7 @@
>>   #include "util.h" // rm_rf_perf_data()
>>   #include "debug.h"
>>   #include "header.h"
>> +#include "evsel.h"
>>   #include <internal/lib.h>
>>
>>   static void close_dir(struct perf_data_file *files, int nr)
>> @@ -35,6 +36,7 @@ void perf_data__close_dir(struct perf_data *data)
>>
>>   int perf_data__create_dir(struct perf_data *data, int nr)
>>   {
>> +       enum rlimit_action set_rlimit = NO_CHANGE;
>>          struct perf_data_file *files = NULL;
>>          int i, ret;
>>
>> @@ -54,11 +56,21 @@ int perf_data__create_dir(struct perf_data *data, int nr)
>>                          goto out_err;
>>                  }
>>
>> +retry_open:
>>                  ret = open(file->path, O_RDWR|O_CREAT|O_TRUNC, S_IRUSR|S_IWUSR);
>>                  if (ret < 0) {
>> +                       /*
>> +                        * If using parallel threads to collect data,
>> +                        * perf record needs at least 6 fds per CPU.
>> +                        * When we run out of them try to increase the limits.
>> +                        */
>> +                       if (errno == EMFILE && evsel__increase_rlimit(&set_rlimit))
> 
> It seems weird that we have this helper with evsel prefix and
> it does nothing with evsel.  But it's a separate concern, so
> 
> Acked-by: Namhyung Kim <namhyung@kernel.org>
Thanks for the Acked-by tag.

Uh... The name of this helper doesn't seem to be appropriate.
Okay, I'll submit a patch to fix this helper name.

Thanks,
Yang