Hi Ingo, On Mon, Dec 14, 2015 at 10:38:41AM +0100, Ingo Molnar wrote: > > * Peter Zijlstra <pet...@infradead.org> wrote: > > > On Fri, Dec 11, 2015 at 08:01:31AM -0700, David Ahern wrote: > > > On 12/11/15 1:11 AM, Ingo Molnar wrote: > > > > > > > >* Namhyung Kim <namhy...@gmail.com> wrote: > > > > > > > >>IIRC David said that thread per cpu seems too much especially on a > > > >>large system > > > >>(like ~1024 cpu). [...] > > > > > > > >Too much in what fashion? For recording I think it's the fastest, most > > > >natural > > > >model - anything else will create cache line bounces. > > > > > > The intrusiveness of perf on the system under observation. I understand > > > there are a lot of factors that go into it. > > > > So I can see some of that, if every cpu has its own thread then every > > cpu will occasionally schedule that thread. Whereas if there were less, > > you'd not have that. > > > > Still, I think it makes sense to implement it, we need the multi-file > > option anyway. Once we have that, we can also implement a per-node > > option, which should be a fairly simple hybrid of the two approaches. > > > > The thing is, perf-record is really struggling on big machines. > > > > And in an unrelated note, I absolutely detest --buildid being the > > default, it makes perf-record blow chunks. > > So I'd absolutely _love_ to split up the singular perf.data into a hierarchy > of > files in a .perf directory, with a structure like this (4-core system): > > .perf/cmdline > .perf/features > .perf/evlist > .perf/ring_buffers/cpu0/raw.trace > .perf/ring_buffers/cpu1/raw.trace > .perf/ring_buffers/cpu2/raw.trace > .perf/ring_buffers/cpu3/raw.trace > ... > > I.e. the current single file format of perf.data would be split up into > individual > files. Each CPU would get its own trace file output - any sorting and > ordering > would be done afterwards. 'perf record' itself would never by default have to > do > any of that, it's a pure recording session. > > 'perf archive' would still create a single file to make transport between > machines > easy. > > perf.data.old would be replaced by a .perf.old directory or so. > > Debugging would be easier too I think, as there's no complex perf data format > anymore, it's all in individual (typically text, or binary dump) files in the > .perf directory. > > This would solve all the scalability problems - and would make the format > more > extensible and generally more accessible as well. > > What do you think?
It requires many changes, but basically I also like the split-up since it's easier to deal with. IIRC there was an opinion (Andi?) regarding single-file vs multi-file. The file access will be better for single file so I changed my earlier implementation to use indexed single data file instead of multiple files. But anyway, I'll work on perf-top first :) Thanks, Namhyung -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
