On Tue, May 7, 2024 at 3:27 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote: > > On Tue, May 7, 2024 at 10:29 AM Andrii Nakryiko > <andrii.nakryiko@xxxxxxxxx> wrote: > > > > On Mon, May 6, 2024 at 10:06 PM Andrii Nakryiko > > <andrii.nakryiko@xxxxxxxxx> wrote: > > > > > > On Mon, May 6, 2024 at 11:43 AM Ian Rogers <irogers@xxxxxxxxxx> wrote: > > > > > > > > On Mon, May 6, 2024 at 11:32 AM Andrii Nakryiko > > > > <andrii.nakryiko@xxxxxxxxx> wrote: > > > > > > > > > > On Sat, May 4, 2024 at 10:09 PM Ian Rogers <irogers@xxxxxxxxxx> wrote: > > > > > > > > > > > > On Sat, May 4, 2024 at 2:57 PM Andrii Nakryiko > > > > > > <andrii.nakryiko@xxxxxxxxx> wrote: > > > > > > > > > > > > > > On Sat, May 4, 2024 at 8:29 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > On Fri, May 03, 2024 at 05:30:06PM -0700, Andrii Nakryiko wrote: > > > > > > > > > Implement a simple tool/benchmark for comparing address "resolution" > > > > > > > > > logic based on textual /proc/<pid>/maps interface and new binary > > > > > > > > > ioctl-based PROCFS_PROCMAP_QUERY command. > > > > > > > > > > > > > > > > Of course an artificial benchmark of "read a whole file" vs. "a tiny > > > > > > > > ioctl" is going to be different, but step back and show how this is > > > > > > > > going to be used in the real world overall. Pounding on this file is > > > > > > > > not a normal operation, right? > > > > > > > > > > > > > > > > > > > > > > It's not artificial at all. It's *exactly* what, say, blazesym library > > > > > > > is doing (see [0], it's Rust and part of the overall library API, I > > > > > > > think C code in this patch is way easier to follow for someone not > > > > > > > familiar with implementation of blazesym, but both implementations are > > > > > > > doing exactly the same sequence of steps). You can do it even less > > > > > > > efficiently by parsing the whole file, building an in-memory lookup > > > > > > > table, then looking up addresses one by one. But that's even slower > > > > > > > and more memory-hungry. So I didn't even bother implementing that, it > > > > > > > would put /proc/<pid>/maps at even more disadvantage. > > > > > > > > > > > > > > Other applications that deal with stack traces (including perf) would > > > > > > > be doing one of those two approaches, depending on circumstances and > > > > > > > level of sophistication of code (and sensitivity to performance). > > > > > > > > > > > > The code in perf doing this is here: > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/util/synthetic-events.c#n440 > > > > > > The code is using the api/io.h code: > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/lib/api/io.h > > > > > > Using perf to profile perf it was observed time was spent allocating > > > > > > buffers and locale related activities when using stdio, so io is a > > > > > > lighter weight alternative, albeit with more verbose code than fscanf. > > > > > > You could add this as an alternate /proc/<pid>/maps reader, we have a > > > > > > similar benchmark in `perf bench internals synthesize`. > > > > > > > > > > > > > > > > If I add a new implementation using this ioctl() into > > > > > perf_event__synthesize_mmap_events(), will it be tested from this > > > > > `perf bench internals synthesize`? I'm not too familiar with perf code > > > > > organization, sorry if it's a stupid question. If not, where exactly > > > > > is the code that would be triggered from benchmark? > > > > > > > > Yes it would be triggered :-) > > > > > > Ok, I don't exactly know how to interpret the results (and what the > > > benchmark is doing), but numbers don't seem to be worse. They actually > > > seem to be a bit better. > > > > > > I pushed my code that adds perf integration to [0]. That commit has > > > results, but I'll post them here (with invocation parameters). > > > perf-ioctl is the version with ioctl()-based implementation, > > > perf-parse is, logically, text-parsing version. Here are the results > > > (and see my notes below the results as well): > > > > > > TEXT-BASED > > > ========== > > > > > > # ./perf-parse bench internals synthesize > > > # Running 'internals/synthesize' benchmark: > > > Computing performance of single threaded perf event synthesis by > > > synthesizing events on the perf process itself: > > > Average synthesis took: 80.311 usec (+- 0.077 usec) > > > Average num. events: 32.000 (+- 0.000) > > > Average time per event 2.510 usec > > > Average data synthesis took: 84.429 usec (+- 0.066 usec) > > > Average num. events: 179.000 (+- 0.000) > > > Average time per event 0.472 usec > > > > > > # ./perf-parse bench internals synthesize > > > # Running 'internals/synthesize' benchmark: > > > Computing performance of single threaded perf event synthesis by > > > synthesizing events on the perf process itself: > > > Average synthesis took: 79.900 usec (+- 0.077 usec) > > > Average num. events: 32.000 (+- 0.000) > > > Average time per event 2.497 usec > > > Average data synthesis took: 84.832 usec (+- 0.074 usec) > > > Average num. events: 180.000 (+- 0.000) > > > Average time per event 0.471 usec > > > > > > # ./perf-parse bench internals synthesize --mt -M 8 > > > # Running 'internals/synthesize' benchmark: > > > Computing performance of multi threaded perf event synthesis by > > > synthesizing events on CPU 0: > > > Number of synthesis threads: 1 > > > Average synthesis took: 36338.100 usec (+- 406.091 usec) > > > Average num. events: 14091.300 (+- 7.433) > > > Average time per event 2.579 usec > > > Number of synthesis threads: 2 > > > Average synthesis took: 37071.200 usec (+- 746.498 usec) > > > Average num. events: 14085.900 (+- 1.900) > > > Average time per event 2.632 usec > > > Number of synthesis threads: 3 > > > Average synthesis took: 33932.300 usec (+- 626.861 usec) > > > Average num. events: 14085.900 (+- 1.900) > > > Average time per event 2.409 usec > > > Number of synthesis threads: 4 > > > Average synthesis took: 33822.700 usec (+- 506.290 usec) > > > Average num. events: 14099.200 (+- 8.761) > > > Average time per event 2.399 usec > > > Number of synthesis threads: 5 > > > Average synthesis took: 33348.200 usec (+- 389.771 usec) > > > Average num. events: 14085.900 (+- 1.900) > > > Average time per event 2.367 usec > > > Number of synthesis threads: 6 > > > Average synthesis took: 33269.600 usec (+- 350.341 usec) > > > Average num. events: 14084.000 (+- 0.000) > > > Average time per event 2.362 usec > > > Number of synthesis threads: 7 > > > Average synthesis took: 32663.900 usec (+- 338.870 usec) > > > Average num. events: 14085.900 (+- 1.900) > > > Average time per event 2.319 usec > > > Number of synthesis threads: 8 > > > Average synthesis took: 32748.400 usec (+- 285.450 usec) > > > Average num. events: 14085.900 (+- 1.900) > > > Average time per event 2.325 usec > > > > > > IOCTL-BASED > > > =========== > > > # ./perf-ioctl bench internals synthesize > > > # Running 'internals/synthesize' benchmark: > > > Computing performance of single threaded perf event synthesis by > > > synthesizing events on the perf process itself: > > > Average synthesis took: 72.996 usec (+- 0.076 usec) > > > Average num. events: 31.000 (+- 0.000) > > > Average time per event 2.355 usec > > > Average data synthesis took: 79.067 usec (+- 0.074 usec) > > > Average num. events: 178.000 (+- 0.000) > > > Average time per event 0.444 usec > > > > > > # ./perf-ioctl bench internals synthesize > > > # Running 'internals/synthesize' benchmark: > > > Computing performance of single threaded perf event synthesis by > > > synthesizing events on the perf process itself: > > > Average synthesis took: 73.921 usec (+- 0.073 usec) > > > Average num. events: 31.000 (+- 0.000) > > > Average time per event 2.385 usec > > > Average data synthesis took: 80.545 usec (+- 0.070 usec) > > > Average num. events: 178.000 (+- 0.000) > > > Average time per event 0.453 usec > > > > > > # ./perf-ioctl bench internals synthesize --mt -M 8 > > > # Running 'internals/synthesize' benchmark: > > > Computing performance of multi threaded perf event synthesis by > > > synthesizing events on CPU 0: > > > Number of synthesis threads: 1 > > > Average synthesis took: 35609.500 usec (+- 428.576 usec) > > > Average num. events: 14040.700 (+- 1.700) > > > Average time per event 2.536 usec > > > Number of synthesis threads: 2 > > > Average synthesis took: 34293.800 usec (+- 453.811 usec) > > > Average num. events: 14040.700 (+- 1.700) > > > Average time per event 2.442 usec > > > Number of synthesis threads: 3 > > > Average synthesis took: 32385.200 usec (+- 363.106 usec) > > > Average num. events: 14040.700 (+- 1.700) > > > Average time per event 2.307 usec > > > Number of synthesis threads: 4 > > > Average synthesis took: 33113.100 usec (+- 553.931 usec) > > > Average num. events: 14054.500 (+- 11.469) > > > Average time per event 2.356 usec > > > Number of synthesis threads: 5 > > > Average synthesis took: 31600.600 usec (+- 297.349 usec) > > > Average num. events: 14012.500 (+- 4.590) > > > Average time per event 2.255 usec > > > Number of synthesis threads: 6 > > > Average synthesis took: 32309.900 usec (+- 472.225 usec) > > > Average num. events: 14004.000 (+- 0.000) > > > Average time per event 2.307 usec > > > Number of synthesis threads: 7 > > > Average synthesis took: 31400.100 usec (+- 206.261 usec) > > > Average num. events: 14004.800 (+- 0.800) > > > Average time per event 2.242 usec > > > Number of synthesis threads: 8 > > > Average synthesis took: 31601.400 usec (+- 303.350 usec) > > > Average num. events: 14005.700 (+- 1.700) > > > Average time per event 2.256 usec > > > > > > I also double-checked (using strace) that it does what it is supposed > > > to do, and it seems like everything checks out. Here's text-based > > > strace log: > > > > > > openat(AT_FDCWD, "/proc/35876/task/35876/maps", O_RDONLY) = 3 > > > read(3, "00400000-0040c000 r--p 00000000 "..., 8192) = 3997 > > > read(3, "7f519d4d3000-7f519d516000 r--p 0"..., 8192) = 4025 > > > read(3, "7f519dc3d000-7f519dc44000 r-xp 0"..., 8192) = 4048 > > > read(3, "7f519dd2d000-7f519dd2f000 r--p 0"..., 8192) = 4017 > > > read(3, "7f519dff6000-7f519dff8000 r--p 0"..., 8192) = 2744 > > > read(3, "", 8192) = 0 > > > close(3) = 0 > > > > > > > > > BTW, note how the kernel doesn't serve more than 4KB of data, even > > > though perf provides 8KB buffer (that's to Greg's question about > > > optimizing using bigger buffers, I suspect without seq_file changes, > > > it won't work). > > > > > > And here's an abbreviated log for ioctl version, it has lots more (but > > > much faster) ioctl() syscalls, given it dumps everything: > > > > > > openat(AT_FDCWD, "/proc/36380/task/36380/maps", O_RDONLY) = 3 > > > ioctl(3, _IOC(_IOC_READ|_IOC_WRITE, 0x9f, 0x1, 0x60), 0x7fff6b603d50) = 0 > > > ioctl(3, _IOC(_IOC_READ|_IOC_WRITE, 0x9f, 0x1, 0x60), 0x7fff6b603d50) = 0 > > > > > > ... 195 ioctl() calls in total ... > > > > > > ioctl(3, _IOC(_IOC_READ|_IOC_WRITE, 0x9f, 0x1, 0x60), 0x7fff6b603d50) = 0 > > > ioctl(3, _IOC(_IOC_READ|_IOC_WRITE, 0x9f, 0x1, 0x60), 0x7fff6b603d50) = 0 > > > ioctl(3, _IOC(_IOC_READ|_IOC_WRITE, 0x9f, 0x1, 0x60), 0x7fff6b603d50) = 0 > > > ioctl(3, _IOC(_IOC_READ|_IOC_WRITE, 0x9f, 0x1, 0x60), 0x7fff6b603d50) > > > = -1 ENOENT (No such file or directory) > > > close(3) = 0 > > > > > > > > > So, it's not the optimal usage of this API, and yet it's still better > > > (or at least not worse) than text-based API. > > It's surprising that more ioctl is cheaper than less read and parse. I encourage you to try this locally, just in case I missed something ([0]). But it does seem this way. I have mitigations and retpoline off, so syscall switch is pretty fast (under 0.5 microsecond). [0] https://github.com/anakryiko/linux/tree/procfs-proc-maps-ioctl > > > > > > > > In another reply to Arnaldo on patch #2 I mentioned the idea of > > allowing to iterate only file-backed VMAs (as it seems like what > > symbolizers would only care about, but I might be wrong here). So I > > Yep, I think it's enough to get file-backed VMAs only. > Ok, I guess I'll keep this functionality for v2 then, it's a pretty trivial extension to existing logic. > > > tried that quickly, given it's a trivial addition to my code. See > > results below (it is slightly faster, but not much, because most of > > VMAs in that benchmark seem to be indeed file-backed anyways), just > > for completeness. I'm not sure if that would be useful/used by perf, > > so please let me know. > > Thanks for doing this. It'd be useful as it provides better synthesizing > performance. The startup latency of perf record is a problem, I need > to take a look if it can be improved more. > > Thanks, > Namhyung > > > > > > As I mentioned above, it's not radically faster in this perf > > benchmark, because we still request about 170 VMAs (vs ~195 if we > > iterate *all* of them), so not a big change. The ratio will vary > > depending on what the process is doing, of course. Anyways, just for > > completeness, I'm not sure if I have to add this "filter" to the > > actual implementation. > > > > # ./perf-filebacked bench internals synthesize > > # Running 'internals/synthesize' benchmark: > > Computing performance of single threaded perf event synthesis by > > synthesizing events on the perf process itself: > > Average synthesis took: 65.759 usec (+- 0.063 usec) > > Average num. events: 30.000 (+- 0.000) > > Average time per event 2.192 usec > > Average data synthesis took: 73.840 usec (+- 0.080 usec) > > Average num. events: 153.000 (+- 0.000) > > Average time per event 0.483 usec > > > > # ./perf-filebacked bench internals synthesize > > # Running 'internals/synthesize' benchmark: > > Computing performance of single threaded perf event synthesis by > > synthesizing events on the perf process itself: > > Average synthesis took: 66.245 usec (+- 0.059 usec) > > Average num. events: 30.000 (+- 0.000) > > Average time per event 2.208 usec > > Average data synthesis took: 70.627 usec (+- 0.074 usec) > > Average num. events: 153.000 (+- 0.000) > > Average time per event 0.462 usec > > > > # ./perf-filebacked bench internals synthesize --mt -M 8 > > # Running 'internals/synthesize' benchmark: > > Computing performance of multi threaded perf event synthesis by > > synthesizing events on CPU 0: > > Number of synthesis threads: 1 > > Average synthesis took: 33477.500 usec (+- 556.102 usec) > > Average num. events: 10125.700 (+- 1.620) > > Average time per event 3.306 usec > > Number of synthesis threads: 2 > > Average synthesis took: 30473.700 usec (+- 221.933 usec) > > Average num. events: 10127.000 (+- 0.000) > > Average time per event 3.009 usec > > Number of synthesis threads: 3 > > Average synthesis took: 29775.200 usec (+- 315.212 usec) > > Average num. events: 10128.700 (+- 0.667) > > Average time per event 2.940 usec > > Number of synthesis threads: 4 > > Average synthesis took: 29477.100 usec (+- 621.258 usec) > > Average num. events: 10129.000 (+- 0.000) > > Average time per event 2.910 usec > > Number of synthesis threads: 5 > > Average synthesis took: 29777.900 usec (+- 294.710 usec) > > Average num. events: 10144.700 (+- 11.597) > > Average time per event 2.935 usec > > Number of synthesis threads: 6 > > Average synthesis took: 27774.700 usec (+- 357.569 usec) > > Average num. events: 10158.500 (+- 14.710) > > Average time per event 2.734 usec > > Number of synthesis threads: 7 > > Average synthesis took: 27437.200 usec (+- 233.626 usec) > > Average num. events: 10135.700 (+- 2.700) > > Average time per event 2.707 usec > > Number of synthesis threads: 8 > > Average synthesis took: 28784.600 usec (+- 477.630 usec) > > Average num. events: 10133.000 (+- 0.000) > > Average time per event 2.841 usec > > > > > [0] https://github.com/anakryiko/linux/commit/0841fe675ed30f5605c5b228e18f5612ea253b35 > > > > > > > > > > > Thanks, > > > > Ian > > > > > > > > > > Thanks, > > > > > > Ian > > > > > > > > > > > > > [0] https://github.com/libbpf/blazesym/blob/ee9b48a80c0b4499118a1e8e5d901cddb2b33ab1/src/normalize/user.rs#L193 > > > > > > > > > > > > > > > thanks, > > > > > > > > > > > > > > > > greg k-h > > > > > > > > >
