在 2024/10/16 2:58, Catalin Marinas 写道: > On Mon, 09 Sep 2024 07:11:14 +0000, Liao Chang wrote: >> v2->v1: >> 1. Remove the simuation of STP and the related bits. >> 2. Use arm64_skip_faulting_instruction for single-stepping or FEAT_BTI >> scenario. >> >> As Andrii pointed out, the uprobe/uretprobe selftest bench run into a >> counterintuitive result that nop and push variants are much slower than >> ret variant [0]. The root cause lies in the arch_probe_analyse_insn(), >> which excludes 'nop' and 'stp' from the emulatable instructions list. >> This force the kernel returns to userspace and execute them out-of-line, >> then trapping back to kernel for running uprobe callback functions. This >> leads to a significant performance overhead compared to 'ret' variant, >> which is already emulated. >> >> [...] > > Applied to arm64 (for-next/probes), thanks! I fixed it up according to > Mark's comments. > > [1/1] arm64: insn: Simulate nop instruction for better uprobe performance > https://git.kernel.org/arm64/c/ac4ad5c09b34 > Mark, Catalin and Andrii, I am just back from a long vacation, thanks for reviewing and involvement for this patch. I've sent a patch [1] that simulates STP at function entry, It maps user stack pages to kernel address space, allowing kernel to use STP directly to push fp/lr onto stack. Unfortunately, the profiling results below show reveals this approach increases the uprobe-push throughput by 29.3% (from 0.868M/s/cpu to 1.1238M/s/cpu) and uretprobe-push by 15.9% (from 0.616M/s/cpu to 0.714M/s/cpu). As Andrii pointed out, this approach is a bit complex and overkill for STP simluation. So I look forward to more input about this patch, is it possible to reach a better result? Or should I pause this work for now and wait for Arm64 to add some instruction for storing pairs of registers to unprivileged memory in privileged exception level? Thanks. xol-stp ------- uprobe-push ( 1 cpus): 0.868 ± 0.001M/s ( 0.868M/s/cpu) uretprobe-push ( 1 cpus): 0.616 ± 0.001M/s ( 0.616M/s/cpu) simulated-stp ------------- uprobe-push ( 1 cpus): 1.128 ± 0.002M/s ( 1.128M/s/cpu) uretprobe-push ( 1 cpus): 0.714 ± 0.001M/s ( 0.714M/s/cpu) [1] https://lore.kernel.org/all/20240910060407.1427716-1-liaochang1@xxxxxxxxxx/ -- BR Liao, Chang
