Messages in this thread |  | | From | Namhyung Kim <> | Subject | Re: [PATCH 4/5] perf record: mmap output file - v5 | Date | Tue, 19 Nov 2013 09:24:48 +0900 |
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Hi Ingo,
On Mon, 18 Nov 2013 10:40:36 +0100, Ingo Molnar wrote: > * Peter Zijlstra <peterz@infradead.org> wrote: > >> On Fri, Nov 15, 2013 at 09:41:53AM -0700, David Ahern wrote: >> > On 11/13/13, 4:34 AM, Peter Zijlstra wrote: >> > >>>one option here is not allow page faults and system wide system calls. >> > >>>system wide tracing needs mmap; page faults for a task can use write(). >> > >>>I left that option in case something like this came up. >> > >> >> > >>So maybe splice() sounds like the right long term solution after all? :-/ >> > > >> > >Right until you put a tracepoint (kprobe) somewhere in whatever function >> > >is used to transfer a single page into/from a splice pipe. >> > > >> > >You can always screw yourself over using this stuff, no exceptions. >> > > >> > >> > 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. :)
Thanks, Namhyung
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