Messages in this thread |  | | Date | Wed, 13 Nov 2013 12:34:39 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 4/5] perf record: mmap output file - v5 |
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On Tue, Nov 12, 2013 at 10:11:21PM +0100, Ingo Molnar wrote: > > * David Ahern <dsahern@gmail.com> wrote: > > > > Dunno.. it _should_ all work. Try it and see what it does.. Once the > > > events are bigger than a page things might get 'interesting' though. > > Which could be the case with call-graph recording, right?
Not typically, I think we're limiting call graphs to 127 u64, which is ~1k. Maybe you can blow the single page if you also do a large top-of-stack copy for dwarf/unwind nonsense.
> > 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.
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