On Mon, Aug 12, 2024 at 4:11 AM Liao, Chang <liaochang1@xxxxxxxxxx> wrote: > > > > 在 2024/8/9 2:26, Andrii Nakryiko 写道: > > On Thu, Aug 8, 2024 at 1:45 AM Liao, Chang <liaochang1@xxxxxxxxxx> wrote: > >> > >> Hi Andrii and Oleg. > >> > >> This patch sent by me two weeks ago also aim to optimize the performance of uprobe > >> on arm64. I notice recent discussions on the performance and scalability of uprobes > >> within the mailing list. Considering this interest, I've added you and other relevant > >> maintainers to the CC list for broader visibility and potential collaboration. > >> > > > > Hi Liao, > > > > As you can see there is an active work to improve uprobes, that > > changes lifetime management of uprobes, removes a bunch of locks taken > > in the uprobe/uretprobe hot path, etc. It would be nice if you can > > hold off a bit with your changes until all that lands. And then > > re-benchmark, as costs might shift. > > > > But also see some remarks below. > > > >> Thanks. > >> > >> 在 2024/7/27 17:44, Liao Chang 写道: > >>> The profiling result of single-thread model of selftests bench reveals > >>> performance bottlenecks in find_uprobe() and caches_clean_inval_pou() on > >>> ARM64. On my local testing machine, 5% of CPU time is consumed by > >>> find_uprobe() for trig-uprobe-ret, while caches_clean_inval_pou() take > >>> about 34% of CPU time for trig-uprobe-nop and trig-uprobe-push. > >>> > >>> This patch introduce struct uprobe_breakpoint to track previously > >>> allocated insn_slot for frequently hit uprobe. it effectively reduce the > >>> need for redundant insn_slot writes and subsequent expensive cache > >>> flush, especially on architecture like ARM64. This patch has been tested > >>> on Kunpeng916 (Hi1616), 4 NUMA nodes, 64 cores@ 2.4GHz. The selftest > >>> bench and Redis GET/SET benchmark result below reveal obivious > >>> performance gain. > >>> > >>> before-opt > >>> ---------- > >>> trig-uprobe-nop: 0.371 ± 0.001M/s (0.371M/prod) > >>> trig-uprobe-push: 0.370 ± 0.001M/s (0.370M/prod) > >>> trig-uprobe-ret: 1.637 ± 0.001M/s (1.647M/prod) > > > > I'm surprised that nop and push variants are much slower than ret > > variant. This is exactly opposite on x86-64. Do you have an > > explanation why this might be happening? I see you are trying to > > optimize xol_get_insn_slot(), but that is (at least for x86) a slow > > variant of uprobe that normally shouldn't be used. Typically uprobe is > > installed on nop (for USDT) and on function entry (which would be push > > variant, `push %rbp` instruction). > > > > ret variant, for x86-64, causes one extra step to go back to user > > space to execute original instruction out-of-line, and then trapping > > back to kernel for running uprobe. Which is what you normally want to > > avoid. > > > > What I'm getting at here. It seems like maybe arm arch is missing fast > > emulated implementations for nops/push or whatever equivalents for > > ARM64 that is. Please take a look at that and see why those are slow > > and whether you can make those into fast uprobe cases? > > Hi Andrii, > > As you correctly pointed out, the benchmark result on Arm64 is counterintuitive > compared to X86 behavior. My investigation revealed that the root cause lies in > the arch_uprobe_analyse_insn(), which excludes the Arm64 equvialents instructions > of 'nop' and 'push' from the emulatable instruction list. This forces the kernel > to handle these instructions out-of-line in userspace upon breakpoint exception > is handled, leading to a significant performance overhead compared to 'ret' variant, > which is already emulated. > > To address this issue, I've developed a patch supports the emulation of 'nop' and > 'push' variants. The benchmark results below indicates the performance gain of > emulation is obivious. > > xol (1 cpus) > ------------ > uprobe-nop: 0.916 ± 0.001M/s (0.916M/prod) > uprobe-push: 0.908 ± 0.001M/s (0.908M/prod) > uprobe-ret: 1.855 ± 0.000M/s (1.855M/prod) > uretprobe-nop: 0.640 ± 0.000M/s (0.640M/prod) > uretprobe-push: 0.633 ± 0.001M/s (0.633M/prod) > uretprobe-ret: 0.978 ± 0.003M/s (0.978M/prod) > > emulation (1 cpus) > ------------------- > uprobe-nop: 1.862 ± 0.002M/s (1.862M/s/cpu) > uprobe-push: 1.743 ± 0.006M/s (1.743M/s/cpu) > uprobe-ret: 1.840 ± 0.001M/s (1.840M/s/cpu) > uretprobe-nop: 0.964 ± 0.004M/s (0.964M/s/cpu) > uretprobe-push: 0.936 ± 0.004M/s (0.936M/s/cpu) > uretprobe-ret: 0.940 ± 0.001M/s (0.940M/s/cpu) > > As you can see, the performance gap between nop/push and ret variants has been significantly > reduced. Due to the emulation of 'push' instruction need to access userspace memory, it spent > more cycles than the other. Great, it's an obvious improvement. Are you going to send patches upstream? Please cc bpf@xxxxxxxxxxxxxxx as well. I'm also thinking we should update uprobe/uretprobe benchmarks to be less x86-specific. Right now "-nop" is the happy fastest case, "-push" is still happy, slightly slower case (due to the need to emulate stack operation) and "-ret" is meant to be the slow single-step case. We should adjust the naming and make sure that on ARM64 we hit similar code paths. Given you seem to know arm64 pretty well, can you please take a look at updating bench tool for ARM64 (we can also rename benchmarks to something a bit more generic, rather than using instruction names)? > > > > >>> trig-uretprobe-nop: 0.331 ± 0.004M/s (0.331M/prod) > >>> trig-uretprobe-push: 0.333 ± 0.000M/s (0.333M/prod) > >>> trig-uretprobe-ret: 0.854 ± 0.002M/s (0.854M/prod) > >>> Redis SET (RPS) uprobe: 42728.52 > >>> Redis GET (RPS) uprobe: 43640.18 > >>> Redis SET (RPS) uretprobe: 40624.54 > >>> Redis GET (RPS) uretprobe: 41180.56 > >>> > >>> after-opt > >>> --------- > >>> trig-uprobe-nop: 0.916 ± 0.001M/s (0.916M/prod) > >>> trig-uprobe-push: 0.908 ± 0.001M/s (0.908M/prod) > >>> trig-uprobe-ret: 1.855 ± 0.000M/s (1.855M/prod) > >>> trig-uretprobe-nop: 0.640 ± 0.000M/s (0.640M/prod) > >>> trig-uretprobe-push: 0.633 ± 0.001M/s (0.633M/prod) > >>> trig-uretprobe-ret: 0.978 ± 0.003M/s (0.978M/prod) > >>> Redis SET (RPS) uprobe: 43939.69 > >>> Redis GET (RPS) uprobe: 45200.80 > >>> Redis SET (RPS) uretprobe: 41658.58 > >>> Redis GET (RPS) uretprobe: 42805.80 > >>> > >>> While some uprobes might still need to share the same insn_slot, this > >>> patch compare the instructions in the resued insn_slot with the > >>> instructions execute out-of-line firstly to decides allocate a new one > >>> or not. > >>> > >>> Additionally, this patch use a rbtree associated with each thread that > >>> hit uprobes to manage these allocated uprobe_breakpoint data. Due to the > >>> rbtree of uprobe_breakpoints has smaller node, better locality and less > >>> contention, it result in faster lookup times compared to find_uprobe(). > >>> > >>> The other part of this patch are some necessary memory management for > >>> uprobe_breakpoint data. A uprobe_breakpoint is allocated for each newly > >>> hit uprobe that doesn't already have a corresponding node in rbtree. All > >>> uprobe_breakpoints will be freed when thread exit. > >>> > >>> Signed-off-by: Liao Chang <liaochang1@xxxxxxxxxx> > >>> --- > >>> include/linux/uprobes.h | 3 + > >>> kernel/events/uprobes.c | 246 +++++++++++++++++++++++++++++++++------- > >>> 2 files changed, 211 insertions(+), 38 deletions(-) > >>> > > > > [...] > > -- > BR > Liao, Chang
