On Mon, Jan 5, 2015 at 1:48 PM, Andi Kleen <[email protected]> wrote: > > > Thanks for working on this. Haven't read any code, just > some high level comments on the design. > > > > So my approach is like this: > > > > Partially do stage 1 first - but only for meta events that changes > > machine state. To do this I add a dummy tracking event to perf record > > and make it collect such meta events only. They are saved in a > > separate file (perf.header) and processed before sample events at perf > > report time. > > Can't you just use seek to put the offset into the perf.data header > like it's already done for other sections? Managing another file would be > a big change for users and especially is a problem if the data > is moved between different systems. > > Also I thought Adrian's meta data index already addressed this > at least partially. > > > > > This also requires to handle multiple files and to find a > > corresponding machine state when processing samples. On a large > > profiling session, many tasks were created and exited so pid might be > > recycled (even more than once!). To deal with it, I managed to have > > thread, map_groups and comm in time sorted. The only remaining thing > > is symbol loading as it's done lazily when sample requires it. > > FWIW there's often a lot of unnecessary information in this > (e.g. mmaps that are not used). The Quipper page > claims large saving in data files by avoided redundancies. > > It would be probably better if perf record avoided writing redundant > information better (I realize that's not easy) > > > > With that being done, the stage 2 can be done by multiple threads. I > > also save each sample data (per-cpu or per-thread) in separate files > > during record. On perf report time, each file will be processed by > > each thread. And symbol loading is protected by a mutex lock. > > I really don't like the multiple files. See above. Also it could easily > cause additional seeking on spinning disks. > having to manage two separate files is a major change which I don't particularly like. It will cause problems. I don't see why this cannot be appended to the perf.data file with a index at the beginning. There is already an index for sections in file mode.
We use the pipe mode a lot and this would not work there. So no, I don't like the 2 files solution. But I like the idea of using multiple threads to speed up processing. > > Isn't it fast enough to have a single thread that pre scans > the events (perhaps with some single-thread optimizations > like vectorization), and then load balances the work to > a thread pool? > > BTW I suspect if you used cilk plus or a similar library that > would make the code much simpler. > > > Here is the result: > > > > This is just elapsed (real) time measured by shell 'time' function. > > > > The data file was recorded during kernel build with fp callchain and > > size is 2.1GB. The machine has 6 core with hyper-threading enabled > > and I got a similar result on my laptop too. > > > > time perf report --children --no-children + --call-graph none > > ---------- ------------- ------------------- > > current 4m43.260s 1m32.779s 0m35.866s > > patched 4m43.710s 1m29.695s 0m33.995s > > --multi-thread 2m46.265s 0m45.486s 0m7.570s > > > > > > This result is with 7.7GB data file using libunwind for callchain. > > Nice results! > > -Andi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
