Hi Florent, On Mon, 17 Oct 2022 19:55:06 +0200 Florent Revest <revest@xxxxxxxxxxxx> wrote: > On Thu, Oct 6, 2022 at 6:29 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > > On Thu, 6 Oct 2022 18:19:12 +0200 > > Florent Revest <revest@xxxxxxxxxxxx> wrote: > > > > > Sure, we can give this a try, I'll work on a macro that generates the > > > 7 callbacks and we can check how much that helps. My belief right now > > > is that ftrace's iteration over all ops on arm64 is where we lose most > > > time but now that we have numbers it's pretty easy to check hypothesis > > > :) > > > > Ah, I forgot that's what Mark's code is doing. But yes, that needs to be > > fixed first. I forget that arm64 doesn't have the dedicated trampolines yet. > > > > So, let's hold off until that is complete. > > > > -- Steve > > Mark finished an implementation of his per-callsite-ops and min-args > branches (meaning that we can now skip the expensive ftrace's saving > of all registers and iteration over all ops if only one is attached) > - https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64-ftrace-call-ops-20221017 > > And Masami wrote similar patches to what I had originally done to > fprobe in my branch: > - https://github.com/mhiramat/linux/commits/kprobes/fprobe-update > > So I could rebase my previous "bpf on fprobe" branch on top of these: > (as before, it's just good enough for benchmarking and to give a > general sense of the idea, not for a thorough code review): > - https://github.com/FlorentRevest/linux/commits/fprobe-min-args-3 > > And I could run the benchmarks against my rpi4. I have different > baseline numbers as Xu so I ran everything again and tried to keep the > format the same. "indirect call" refers to my branch I just linked and > "direct call" refers to the series this is a reply to (Xu's work) Thanks for sharing the measurement results. Yes, fprobes/rethook implementation is just porting the kretprobes implementation, thus it may not be so optimized. BTW, I remember Wuqiang's patch for kretprobes. https://lore.kernel.org/all/20210830173324.32507-1-wuqiang.matt@xxxxxxxxxxxxx/T/#u This is for the scalability fixing, but may possible to improve the performance a bit. It is not hard to port to the recent kernel. Can you try it too? Anyway, eventually, I would like to remove the current kretprobe based implementation and unify fexit hook with function-graph tracer. It should make more better perfromance on it. Thank you, > > 1. test with dd > > 1.1 when no bpf prog attached to vfs_write > > # dd if=/dev/zero of=/dev/null count=1000000 > 1000000+0 records in > 1000000+0 records out > 512000000 bytes (512 MB, 488 MiB) copied, 3.94315 s, 130 MB/s > > > 1.2 attach bpf prog with kprobe, bpftrace -e kprobe:vfs_write {} > > # dd if=/dev/zero of=/dev/null count=1000000 > 1000000+0 records in > 1000000+0 records out > 512000000 bytes (512 MB, 488 MiB) copied, 5.80493 s, 88.2 MB/s > > > 1.3 attach bpf prog with with direct call, bpftrace -e kfunc:vfs_write {} > > # dd if=/dev/zero of=/dev/null count=1000000 > 1000000+0 records in > 1000000+0 records out > 512000000 bytes (512 MB, 488 MiB) copied, 4.18579 s, 122 MB/s > > > 1.4 attach bpf prog with with indirect call, bpftrace -e kfunc:vfs_write {} > > # dd if=/dev/zero of=/dev/null count=1000000 > 1000000+0 records in > 1000000+0 records out > 512000000 bytes (512 MB, 488 MiB) copied, 4.92616 s, 104 MB/s > > > 2. test with bpf/bench > > 2.1 bench trig-base > Iter 0 ( 86.518us): hits 0.700M/s ( 0.700M/prod), drops > 0.000M/s, total operations 0.700M/s > Iter 1 (-26.352us): hits 0.701M/s ( 0.701M/prod), drops > 0.000M/s, total operations 0.701M/s > Iter 2 ( 1.092us): hits 0.701M/s ( 0.701M/prod), drops > 0.000M/s, total operations 0.701M/s > Iter 3 ( -1.890us): hits 0.701M/s ( 0.701M/prod), drops > 0.000M/s, total operations 0.701M/s > Iter 4 ( -2.315us): hits 0.701M/s ( 0.701M/prod), drops > 0.000M/s, total operations 0.701M/s > Iter 5 ( 4.184us): hits 0.701M/s ( 0.701M/prod), drops > 0.000M/s, total operations 0.701M/s > Iter 6 ( -3.241us): hits 0.701M/s ( 0.701M/prod), drops > 0.000M/s, total operations 0.701M/s > Summary: hits 0.701 ± 0.000M/s ( 0.701M/prod), drops 0.000 ± > 0.000M/s, total operations 0.701 ± 0.000M/s > > 2.2 bench trig-kprobe > Iter 0 ( 96.833us): hits 0.290M/s ( 0.290M/prod), drops > 0.000M/s, total operations 0.290M/s > Iter 1 (-20.834us): hits 0.291M/s ( 0.291M/prod), drops > 0.000M/s, total operations 0.291M/s > Iter 2 ( -2.426us): hits 0.291M/s ( 0.291M/prod), drops > 0.000M/s, total operations 0.291M/s > Iter 3 ( 22.332us): hits 0.292M/s ( 0.292M/prod), drops > 0.000M/s, total operations 0.292M/s > Iter 4 (-18.204us): hits 0.292M/s ( 0.292M/prod), drops > 0.000M/s, total operations 0.292M/s > Iter 5 ( 5.370us): hits 0.292M/s ( 0.292M/prod), drops > 0.000M/s, total operations 0.292M/s > Iter 6 ( -7.853us): hits 0.290M/s ( 0.290M/prod), drops > 0.000M/s, total operations 0.290M/s > Summary: hits 0.291 ± 0.001M/s ( 0.291M/prod), drops 0.000 ± > 0.000M/s, total operations 0.291 ± 0.001M/s > > 2.3 bench trig-fentry, with direct call > Iter 0 ( 86.481us): hits 0.530M/s ( 0.530M/prod), drops > 0.000M/s, total operations 0.530M/s > Iter 1 (-12.593us): hits 0.536M/s ( 0.536M/prod), drops > 0.000M/s, total operations 0.536M/s > Iter 2 ( -5.760us): hits 0.532M/s ( 0.532M/prod), drops > 0.000M/s, total operations 0.532M/s > Iter 3 ( 1.629us): hits 0.532M/s ( 0.532M/prod), drops > 0.000M/s, total operations 0.532M/s > Iter 4 ( -1.945us): hits 0.533M/s ( 0.533M/prod), drops > 0.000M/s, total operations 0.533M/s > Iter 5 ( -1.297us): hits 0.532M/s ( 0.532M/prod), drops > 0.000M/s, total operations 0.532M/s > Iter 6 ( 0.444us): hits 0.535M/s ( 0.535M/prod), drops > 0.000M/s, total operations 0.535M/s > Summary: hits 0.533 ± 0.002M/s ( 0.533M/prod), drops 0.000 ± > 0.000M/s, total operations 0.533 ± 0.002M/s > > 2.3 bench trig-fentry, with indirect call > Iter 0 ( 84.463us): hits 0.404M/s ( 0.404M/prod), drops > 0.000M/s, total operations 0.404M/s > Iter 1 (-16.260us): hits 0.405M/s ( 0.405M/prod), drops > 0.000M/s, total operations 0.405M/s > Iter 2 ( -1.038us): hits 0.405M/s ( 0.405M/prod), drops > 0.000M/s, total operations 0.405M/s > Iter 3 ( -3.797us): hits 0.405M/s ( 0.405M/prod), drops > 0.000M/s, total operations 0.405M/s > Iter 4 ( -0.537us): hits 0.402M/s ( 0.402M/prod), drops > 0.000M/s, total operations 0.402M/s > Iter 5 ( 3.536us): hits 0.403M/s ( 0.403M/prod), drops > 0.000M/s, total operations 0.403M/s > Iter 6 ( 12.203us): hits 0.404M/s ( 0.404M/prod), drops > 0.000M/s, total operations 0.404M/s > Summary: hits 0.404 ± 0.001M/s ( 0.404M/prod), drops 0.000 ± > 0.000M/s, total operations 0.404 ± 0.001M/s > > > 3. perf report of bench trig-fentry > > 3.1 with direct call > > 98.67% 0.27% bench bench > [.] trigger_producer > | > --98.40%--trigger_producer > | > |--96.63%--syscall > | | > | --71.90%--el0t_64_sync > | el0t_64_sync_handler > | el0_svc > | do_el0_svc > | | > | |--70.94%--el0_svc_common > | | | > | | > |--29.55%--invoke_syscall > | | | | > | | | > |--26.23%--__arm64_sys_getpgid > | | | | > | > | | | | > |--18.88%--bpf_trampoline_6442462665_0 > | | | | > | | > | | | | > | |--6.85%--__bpf_prog_enter > | | | | > | | | > | | | | > | | --2.68%--migrate_disable > | | | | > | | > | | | | > | |--5.28%--__bpf_prog_exit > | | | | > | | | > | | | | > | | --1.29%--migrate_enable > | | | | > | | > | | | | > | > |--3.96%--bpf_prog_21856463590f61f1_bench_trigger_fentry > | | | | > | | > | | | | > | --0.61%--__rcu_read_lock > | | | | > | > | | | | > --4.42%--find_task_by_vpid > | | | | > | > | | | | > |--2.53%--radix_tree_lookup > | | | | > | > | | | | > --0.61%--idr_find > | | | | > | | | > --0.81%--pid_vnr > | | | > | | > --0.53%--__arm64_sys_getpgid > | | > | --0.95%--invoke_syscall > | > --0.99%--syscall@plt > > > 3.2 with indirect call > > 98.68% 0.20% bench bench > [.] trigger_producer > | > --98.48%--trigger_producer > | > --97.47%--syscall > | > --76.11%--el0t_64_sync > el0t_64_sync_handler > el0_svc > do_el0_svc > | > |--75.52%--el0_svc_common > | | > | > |--46.35%--invoke_syscall > | | | > | | > --44.06%--__arm64_sys_getpgid > | | > | > | | > |--35.40%--ftrace_caller > | | > | | > | | > | --34.04%--fprobe_handler > | | > | | > | | > | |--15.61%--bpf_fprobe_entry > | | > | | | > | | > | | |--3.79%--__bpf_prog_enter > | | > | | | | > | | > | | | > --0.80%--migrate_disable > | | > | | | > | | > | | |--3.74%--__bpf_prog_exit > | | > | | | | > | | > | | | > --0.77%--migrate_enable > | | > | | | > | | > | | > --2.65%--bpf_prog_21856463590f61f1_bench_trigger_fentry > | | > | | > | | > | |--12.65%--rethook_trampoline_handler > | | > | | > | | > | |--1.70%--rethook_try_get > | | > | | | > | | > | | --1.48%--rcu_is_watching > | | > | | > | | > | |--1.46%--freelist_try_get > | | > | | > | | > | --0.65%--rethook_recycle > | | > | > | | > --6.36%--find_task_by_vpid > | | > | > | | > |--3.64%--radix_tree_lookup > | | > | > | | > --1.74%--idr_find > | | > | --1.05%--ftrace_caller > | > --0.59%--invoke_syscall > > This looks slightly better than before but it is actually still a > pretty significant performance hit compared to direct calls. > > Note that I can't really make sense of the perf report with indirect > calls. it always reports it spent 12% of the time in > rethook_trampoline_handler but I verified with both a WARN in that > function and a breakpoint with a debugger, this function does *not* > get called when running this "bench trig-fentry" benchmark. Also it > wouldn't make sense for fprobe_handler to call it so I'm quite > confused why perf would report this call and such a long time spent > there. Anyone know what I could be missing here ? -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
