On Mon, Sep 14, 2020 at 10:26:05AM -0700, Stephane Eranian wrote: > On Mon, Sep 14, 2020 at 2:08 AM <pet...@infradead.org> wrote: > > > > On Sun, Sep 13, 2020 at 11:41:00PM -0700, Stephane Eranian wrote: > > > On Sun, Sep 13, 2020 at 2:03 PM Jiri Olsa <jo...@kernel.org> wrote: > > > what happens if I set mmap3 and mmap2? > > > > > > I think using mmap3 for every mmap may be overkill as you add useless > > > 20 bytes to an mmap record. > > > I am not sure if your code handles the case where mmap3 is not needed > > > because there is no buildid, e.g, anonymous memory. > > > It seems to me you've written the patch in such a way that if the user > > > tool supports mmap3, then it supersedes mmap2, and thus > > > you need all the fields of mmap2. But if could be more interesting to > > > return either MMAP2 or MMAP3 depending on tool support > > > and type of mmap, that would certainly save 20 bytes on any anon mmap. > > > But maybe that logic is already in your patch and I missed it. > > > > That, and what if you don't want any of that buildid nonsense at all? I > > always kill that because it makes perf pointlessly slow and has > > absolutely no upsides for me. > > > I have seen situations where the perf tool takes a visibly significant > amount of time (many seconds) to inject the buildids at the end of the > collection > of perf record (same if using perf inject -b). That is because it > needs to go through all the records in the perf.data to find MMAP > records and then read > the buildids from the filesystem. This has caused some problems in our > environment. Having the kernel add the buildid to *relevant* mmaps > would avoid > a lot of that penalty, by avoiding having to parse the perf.data file > and leveraging the fact that the buildid may be in memory already. > Although my concern on > this has to do with large pages and the impact they have on alignment > of sections in memory. I think Ian can comment better on this. > > I think this patch series is useful if it can demonstrate a speedup > during recording (perf record or perf record | perf inject -b). But it
I haven't meassured, but I assume skipping of perf.data search at the end of the record will make up for reading buildid for each mmap event.. migt be tricky in mmap events heavy workloads > needs to be > optimized to minimize the volume of useless info returned. And Jiri > needs to decide if MMAP3 is a replacement of MMAP2, or a different > kind of record > targeted at ELF images only in which case some of the fields may be > removed. My tendency would be to go for the latter. yes, I like the latter as well, let's see thanks, jirka
