Re: [PATCH 47/48] perf record: Spread maps for --threads option

From: Namhyung Kim
Date: Mon Sep 17 2018 - 07:40:52 EST

On Thu, Sep 13, 2018 at 02:54:49PM +0200, Jiri Olsa wrote:
> Currently we assign all maps to main thread. Adding
> code that spreads maps for --threads option.
> For --thread option we create as many threads as there
> are memory maps in evlist, which is the number of CPUs
> in the system or CPUs we monitor. Each thread gets a
> single data mmap to read.
> In addition we have also same amount of tracking mmaps
> for auxiliary events which we don't create special thread
> for. Instead we assign the to the main thread, because
> there's not much traffic expected there.
> The assignment is visible from --thread-stats output:
> pid write poll skip maps (size 20K)
> 1s 9770 144B 1 0 19K 19K 19K 18K 19K
> 9772 0B 1 0 18K
> 9773 0B 1 0 19K
> 9774 0B 1 0 19K
> There are 5 maps for thread 9770 (1 data map and 4 auxiliary)
> and one data map for every other thread. Each thread writes
> data to the separate data file.

Hmm.. not sure it'll work well for large machines with 1000+ cpus.
What about giving each thread a data mmap and a tracking mmap?


> In addition we also pin every thread to the cpu that
> the data map belongs to in order to keep both writer
> (kernel) and reader (perf tool thread) on the same CPU.
> Link:
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>