Re: [PATCH 4/5] perf record: mmap output file - v5

From: David Ahern
Date: Mon Nov 18 2013 - 19:34:57 EST


On 11/18/13, 5:24 PM, Namhyung Kim wrote:
What now? Can we add the mmap path as an option?

I'd say an option is always a possibility, but someone please try
what happens if you use stupid large events (dwarf stack copies) on
PERF_COUNT_SW_PAGE_FAULTS (.period=1) while recording with mmap().

The other option is to simply disallow PERF_SAMPLE_STACK_USER for
that event.

Personally I think 8k copies for every event are way stupid anyway,
that's a metric ton of data at a huge cost.

Well, with 1 khz sampling of a single threaded workload it's 8MB per
second - that's 80 MB for 10 seconds profiling - not the end of the
world.

We now use 4 khz sampling frequency by default, just FYI. :)

I think Peter is asking about:
perf record -e faults -c 1 --call-graph dwarf,8192 -a -- sleep 1

And as expected it is a massive feedback spiraling out of control.

David
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/