The profiling result of BPF selftest on ARM64 platform reveals the significant contention on the current->sighand->siglock within the handle_singlestep() is the scalability bottleneck. The reason is also very straightforward that all producer threads of benchmark have to contend the spinlock mentioned to resume the TIF_SIGPENDING bit in the thread_info that might be removed in uprobe_deny_signal().
This patch introduces UTASK_SSTEP_DENY_SIGNAL to mark TIF_SIGPENDING is suppress temporarily during the uprobe single-step. Upon uprobe single-step is handled and UTASK_SSTEP_DENY_SIGNAL is confirmed, it could resume the TIF_SIGPENDING directly without acquiring the siglock in most case, then reducing contention and improving overall performance. I've use the script developed by Andrii in [1] to run benchmark. The CPU used was Kunpeng916 (Hi1616), 4 NUMA nodes, 64 cores@2.4GHz running upstream kernel v6.11-rc1 + my optimization [2] for get_xol_insn_slot(). before-opt ---------- uprobe-nop ( 1 cpus): 0.907 ± 0.003M/s ( 0.907M/s/cpu) uprobe-nop ( 2 cpus): 1.676 ± 0.008M/s ( 0.838M/s/cpu) uprobe-nop ( 4 cpus): 3.210 ± 0.003M/s ( 0.802M/s/cpu) uprobe-nop ( 8 cpus): 4.457 ± 0.003M/s ( 0.557M/s/cpu) uprobe-nop (16 cpus): 3.724 ± 0.011M/s ( 0.233M/s/cpu) uprobe-nop (32 cpus): 2.761 ± 0.003M/s ( 0.086M/s/cpu) uprobe-nop (64 cpus): 1.293 ± 0.015M/s ( 0.020M/s/cpu) uprobe-push ( 1 cpus): 0.883 ± 0.001M/s ( 0.883M/s/cpu) uprobe-push ( 2 cpus): 1.642 ± 0.005M/s ( 0.821M/s/cpu) uprobe-push ( 4 cpus): 3.086 ± 0.002M/s ( 0.771M/s/cpu) uprobe-push ( 8 cpus): 3.390 ± 0.003M/s ( 0.424M/s/cpu) uprobe-push (16 cpus): 2.652 ± 0.005M/s ( 0.166M/s/cpu) uprobe-push (32 cpus): 2.713 ± 0.005M/s ( 0.085M/s/cpu) uprobe-push (64 cpus): 1.313 ± 0.009M/s ( 0.021M/s/cpu) uprobe-ret ( 1 cpus): 1.774 ± 0.000M/s ( 1.774M/s/cpu) uprobe-ret ( 2 cpus): 3.350 ± 0.001M/s ( 1.675M/s/cpu) uprobe-ret ( 4 cpus): 6.604 ± 0.000M/s ( 1.651M/s/cpu) uprobe-ret ( 8 cpus): 6.706 ± 0.005M/s ( 0.838M/s/cpu) uprobe-ret (16 cpus): 5.231 ± 0.001M/s ( 0.327M/s/cpu) uprobe-ret (32 cpus): 5.743 ± 0.003M/s ( 0.179M/s/cpu) uprobe-ret (64 cpus): 4.726 ± 0.016M/s ( 0.074M/s/cpu) after-opt --------- uprobe-nop ( 1 cpus): 0.985 ± 0.002M/s ( 0.985M/s/cpu) uprobe-nop ( 2 cpus): 1.773 ± 0.005M/s ( 0.887M/s/cpu) uprobe-nop ( 4 cpus): 3.304 ± 0.001M/s ( 0.826M/s/cpu) uprobe-nop ( 8 cpus): 5.328 ± 0.002M/s ( 0.666M/s/cpu) uprobe-nop (16 cpus): 6.475 ± 0.002M/s ( 0.405M/s/cpu) uprobe-nop (32 cpus): 4.831 ± 0.082M/s ( 0.151M/s/cpu) uprobe-nop (64 cpus): 2.564 ± 0.053M/s ( 0.040M/s/cpu) uprobe-push ( 1 cpus): 0.964 ± 0.001M/s ( 0.964M/s/cpu) uprobe-push ( 2 cpus): 1.766 ± 0.002M/s ( 0.883M/s/cpu) uprobe-push ( 4 cpus): 3.290 ± 0.009M/s ( 0.823M/s/cpu) uprobe-push ( 8 cpus): 4.670 ± 0.002M/s ( 0.584M/s/cpu) uprobe-push (16 cpus): 5.197 ± 0.004M/s ( 0.325M/s/cpu) uprobe-push (32 cpus): 5.068 ± 0.161M/s ( 0.158M/s/cpu) uprobe-push (64 cpus): 2.605 ± 0.026M/s ( 0.041M/s/cpu) uprobe-ret ( 1 cpus): 1.833 ± 0.001M/s ( 1.833M/s/cpu) uprobe-ret ( 2 cpus): 3.384 ± 0.003M/s ( 1.692M/s/cpu) uprobe-ret ( 4 cpus): 6.677 ± 0.004M/s ( 1.669M/s/cpu) uprobe-ret ( 8 cpus): 6.854 ± 0.005M/s ( 0.857M/s/cpu) uprobe-ret (16 cpus): 6.508 ± 0.006M/s ( 0.407M/s/cpu) uprobe-ret (32 cpus): 5.793 ± 0.009M/s ( 0.181M/s/cpu) uprobe-ret (64 cpus): 4.743 ± 0.016M/s ( 0.074M/s/cpu) Above benchmark results demonstrates a obivious improvement in the scalability of trig-uprobe-nop and trig-uprobe-push, the peak throughput of which are from 4.5M/s to 6.4M/s and 3.3M/s to 5.1M/s individually. [1] https://lore.kernel.org/all/20240731214256.3588718-1-and...@kernel.org [2] https://lore.kernel.org/all/20240727094405.1362496-1-liaocha...@huawei.com Signed-off-by: Liao Chang <liaocha...@huawei.com> --- include/linux/uprobes.h | 1 + kernel/events/uprobes.c | 18 +++++++++++------- 2 files changed, 12 insertions(+), 7 deletions(-) diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h index b503fafb7fb3..50acbf96bccd 100644 --- a/include/linux/uprobes.h +++ b/include/linux/uprobes.h @@ -53,6 +53,7 @@ enum uprobe_task_state { UTASK_SSTEP, UTASK_SSTEP_ACK, UTASK_SSTEP_TRAPPED, + UTASK_SSTEP_DENY_SIGNAL, }; /* diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 76a51a1f51e2..4f9c10b3c7b9 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -1980,6 +1980,7 @@ bool uprobe_deny_signal(void) if (task_sigpending(t)) { clear_tsk_thread_flag(t, TIF_SIGPENDING); + utask->state = UTASK_SSTEP_DENY_SIGNAL; if (__fatal_signal_pending(t) || arch_uprobe_xol_was_trapped(t)) { utask->state = UTASK_SSTEP_TRAPPED; @@ -2276,22 +2277,25 @@ static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs) int err = 0; uprobe = utask->active_uprobe; - if (utask->state == UTASK_SSTEP_ACK) + switch (utask->state) { + case UTASK_SSTEP_ACK: err = arch_uprobe_post_xol(&uprobe->arch, regs); - else if (utask->state == UTASK_SSTEP_TRAPPED) + break; + case UTASK_SSTEP_TRAPPED: arch_uprobe_abort_xol(&uprobe->arch, regs); - else + fallthrough; + case UTASK_SSTEP_DENY_SIGNAL: + set_tsk_thread_flag(current, TIF_SIGPENDING); + break; + default: WARN_ON_ONCE(1); + } put_uprobe(uprobe); utask->active_uprobe = NULL; utask->state = UTASK_RUNNING; xol_free_insn_slot(current); - spin_lock_irq(¤t->sighand->siglock); - recalc_sigpending(); /* see uprobe_deny_signal() */ - spin_unlock_irq(¤t->sighand->siglock); - if (unlikely(err)) { uprobe_warn(current, "execute the probed insn, sending SIGILL."); force_sig(SIGILL); -- 2.34.1
