Message-ID: <2c23e9cc-5593-84d0-9157-1e946df941d9@huawei.com>
Date: Wed, 14 Aug 2024 12:17:27 +0800
From: "Liao, Chang" <liaochang1@...wei.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
CC: <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
	<namhyung@...nel.org>, <mark.rutland@....com>,
	<alexander.shishkin@...ux.intel.com>, <jolsa@...nel.org>,
	<irogers@...gle.com>, <adrian.hunter@...el.com>, <kan.liang@...ux.intel.com>,
	"oleg@...hat.com >> Oleg Nesterov" <oleg@...hat.com>, Andrii Nakryiko
	<andrii@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>, Steven Rostedt
	<rostedt@...dmis.org>, <paulmck@...nel.org>, <linux-kernel@...r.kernel.org>,
	<linux-perf-users@...r.kernel.org>, <bpf@...r.kernel.org>,
	<linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH] uprobes: Optimize the allocation of insn_slot for
 performance



在 2024/8/13 1:49, Andrii Nakryiko 写道:
> On Mon, Aug 12, 2024 at 4:11 AM Liao, Chang <liaochang1@...wei.com> wrote:
>>
>>
>>
>> 在 2024/8/9 2:26, Andrii Nakryiko 写道:
>>> On Thu, Aug 8, 2024 at 1:45 AM Liao, Chang <liaochang1@...wei.com> 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@...r.kernel.org as well.

I'll need more time to thoroughly test this patch. The emulation o push/nop
instructions also impacts the kprobe/kretprobe paths on Arm64, As as result,
I'm working on enhancements to trig-kprobe/kretprobe to prevent performance
regression.

> 
> 
> 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)?

Let me use a matrix below for the structured comparsion of uprobe/uretprobe
benchmarks on X86 and Arm64:

Architecture  Instrution Type   Handling method   Performance
X86           nop               Emulated          Fastest
X86           push              Emulated          Fast
X86           ret               Single-step       Slow
Arm64         nop               Emulated          Fastest
Arm64         push              Emulated          Fast
Arm64         ret               Emulated          Faster

I suggest categorize benchmarks into 'emu' for emulated instructions and 'ss'
for 'single-steppable' instructions. Generally, emulated instructions should
outperform single-step ones across different architectures. Regarding the
generic naming, I propose using a self-explanatory style, such as
s/nop/empty-insn/g, s/push/push-stack/g, s/ret/func-return/g.

Above all, example "bench --list" output:

X86:
  ...
  trig-uprobe-emu-empty-insn
  trig-uprobe-ss-func-return
  trig-uprobe-emu-push-stack
  trig-uretprobe-emu-empyt-insn
  trig-uretprobe-ss-func-return
  trig-uretprobe-emu-push-stack
  ...

Arm64:
  ...
  trig-uprobe-emu-empty-insn
  trig-uprobe-emu-func-return
  trig-uprobe-emu-push-stack
  trig-uretprobe-emu-empyt-insn
  trig-uretprobe-emu-func-return
  trig-uretprobe-emu-push-stack
  ...

This structure will allow for direct comparison of uprobe/uretprobe
performance across different architectures and instruction types.
Please let me know your thought, Andrii.

Thanks.

> 
>>
>>>
>>>>> 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@...wei.com>
>>>>> ---
>>>>>  include/linux/uprobes.h |   3 +
>>>>>  kernel/events/uprobes.c | 246 +++++++++++++++++++++++++++++++++-------
>>>>>  2 files changed, 211 insertions(+), 38 deletions(-)
>>>>>
>>>
>>> [...]
>>
>> --
>> BR
>> Liao, Chang

-- 
BR
Liao, Chang

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