linux-kernel - Re: [PATCH v2] uprobes: Improve the usage of xol slots for better scalability

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Message-ID: <CAEf4BzbJZ72Yr6tQuGLpz6fpKFXeUw3cD1BRO3T3j1psV4Qkdg@mail.gmail.com>
Date: Wed, 6 Nov 2024 08:27:19 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: "Liao, Chang" <liaochang1@...wei.com>
Cc: andrii@...nel.org, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org, 
	bpf@...r.kernel.org, Mark Rutland <mark.rutland@....com>, 
	Peter Zijlstra <peterz@...radead.org>, Oleg Nesterov <oleg@...hat.com>, 
	Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v2] uprobes: Improve the usage of xol slots for better scalability

On Wed, Nov 6, 2024 at 1:12 AM Liao, Chang <liaochang1@...wei.com> wrote:
>
>
>
> 在 2024/9/27 17:45, Liao Chang 写道:
> >>  2 files changed, 139 insertions(+), 42 deletions(-)
> >>
> > Liao,
> >
> > Assuming your ARM64 improvements go through, would you still need
> > these changes? XOL case is a slow case and if possible should be
> > avoided at all costs. If all common cases for ARM64 are covered
> > through instruction emulation, would we need to add all this
> > complexity to optimize slow case?
>
> Andrii,
>
> I've studied the optimizations merged over the past month, it seems
> that part of the problem addressed in this patch has been resolved
> by Oleg(uprobes: kill xol_area->slot_count). And I hope you've received
> the email with the re-run results for -push using simulated STP on
> the latest kernel (tag next-20241104). It show significant improvements,
> althought there's still room to match the throughput of -nop and -ret.
> So based on these results, I would prioritize the STP simulation patch.

Great, I was hoping that Oleg's patches would help. And yes, I
absolutely agree, STP simulation to avoid kernel->user->kernel switch
is probably the biggest bang for the buck for ARM64 specifically now.
Can you please send a fastest simulation approach that works like
x86-64, and we can try to continue conversation on the refreshed
patch?

>
> --
> BR
> Liao, Chang
>