Changing frequency rate to perf mem

[Harald Servat <harald.servat@bsc.es>]

Hello list,

   I'm interested on changing the frequency rate to the perf mem tool. I 
understand that this tool captures the data every N loads or stores, 
however I don't see how to tune N.

   I've looked into builtin-record.c approx line 980 and I found that 
changing rec->opts.freq allows me capturing more or less data. 
Initially, its value is 4000 and generates 4.5Mbytes for an application. 
If I modify this value to 200, it generates 0.2Mbytes, therefore 
200/4000 is closely 0.2/4.5 which seems the value I want to tune.

   I'd like to know what is this rec->opts.freq with respect to perf 
mem. I expected to setup the number of loads, therefore the higher N the 
lesser number of samples generated, but it seems the other way around. 
Where I can get any hint on what does this mean.

   BTW, I tried to change this value by adding "-F" and "200" into the 
argv that is passed to cmd_report by adding

         rec_argv[i++] = strdup("-F");
         rec_argv[i++] = strdup("200");

   into line 42 of perf-mem.c - just after the strdup("record"). 
Unfortunately, this seems to break something and perf segfaults often. 
Which is the most appropriate way to tune the user frequency of perf mem?

Thank you very much in advance!

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