Re: [PATCH v3 2/2] uprobes: Remove the spinlock within handle_singlestep()

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

Hi Liao,

On Thu, 15 Aug 2024 01:46:29 +0000
Liao Chang <liaochang1@huawei.com> wrote:

> This patch introduces a flag to track TIF_SIGPENDING is suppress
> temporarily during the uprobe single-step. Upon uprobe singlestep is
> handled and the flag 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 the
> kernel on next tree + the optimization for get_xol_insn_slot() [2].
> 
> 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-andrii@kernel.org
> [2] https://lore.kernel.org/all/20240727094405.1362496-1-liaochang1@huawei.com
> 

This looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thanks,

> Acked-by: Oleg Nesterov <oleg@redhat.com>
> Signed-off-by: Liao Chang <liaochang1@huawei.com>
> ---
>  include/linux/uprobes.h | 1 +
>  kernel/events/uprobes.c | 8 +++++---
>  2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index b503fafb7fb3..e4f57117d9c3 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -75,6 +75,7 @@ struct uprobe_task {
>  
>  	struct uprobe			*active_uprobe;
>  	unsigned long			xol_vaddr;
> +	bool				signal_denied;
>  
>  	struct return_instance		*return_instances;
>  	unsigned int			depth;
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 76a51a1f51e2..589aa2af1a99 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1979,6 +1979,7 @@ bool uprobe_deny_signal(void)
>  	WARN_ON_ONCE(utask->state != UTASK_SSTEP);
>  
>  	if (task_sigpending(t)) {
> +		utask->signal_denied = true;
>  		clear_tsk_thread_flag(t, TIF_SIGPENDING);
>  
>  		if (__fatal_signal_pending(t) || arch_uprobe_xol_was_trapped(t)) {
> @@ -2288,9 +2289,10 @@ static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
>  	utask->state = UTASK_RUNNING;
>  	xol_free_insn_slot(current);
>  
> -	spin_lock_irq(&current->sighand->siglock);
> -	recalc_sigpending(); /* see uprobe_deny_signal() */
> -	spin_unlock_irq(&current->sighand->siglock);
> +	if (utask->signal_denied) {
> +		set_thread_flag(TIF_SIGPENDING);
> +		utask->signal_denied = false;
> +	}
>  
>  	if (unlikely(err)) {
>  		uprobe_warn(current, "execute the probed insn, sending SIGILL.");
> -- 
> 2.34.1
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>