Re: [PATCH 1/2] uprobes: Optimize the return_instance related routines

[Liao, Chang]

在 2024/7/11 5:21, Andrii Nakryiko 写道:
> On Wed, Jul 10, 2024 at 1:19 AM Liao, Chang <liaochang1@xxxxxxxxxx> wrote:
>>
>>
>>
>> 在 2024/7/10 7:55, Andrii Nakryiko 写道:
>>> On Mon, Jul 8, 2024 at 6:00 PM Liao Chang <liaochang1@xxxxxxxxxx> wrote:
>>>>
>>>> Reduce the runtime overhead for struct return_instance data managed by
>>>> uretprobe. This patch replaces the dynamic allocation with statically
>>>> allocated array, leverage two facts that are limited nesting depth of
>>>> uretprobe (max 64) and the function call style of return_instance usage
>>>> (create at entry, free at exit).
>>>>
>>>> This patch has been tested on Kunpeng916 (Hi1616), 4 NUMA nodes, 64
>>>> cores @ 2.4GHz. Redis benchmarks show a throughput gain by 2% for Redis
>>>> GET and SET commands:
>>>>
>>>> ------------------------------------------------------------------
>>>> Test case       | No uretprobes | uretprobes     | uretprobes
>>>>                 |               | (current)      | (optimized)
>>>> ==================================================================
>>>> Redis SET (RPS) | 47025         | 40619 (-13.6%) | 41529 (-11.6%)
>>>> ------------------------------------------------------------------
>>>> Redis GET (RPS) | 46715         | 41426 (-11.3%) | 42306 (-9.4%)
>>>> ------------------------------------------------------------------
>>>>
>>>> Signed-off-by: Liao Chang <liaochang1@xxxxxxxxxx>
>>>> ---
>>>>  include/linux/uprobes.h |  10 ++-
>>>>  kernel/events/uprobes.c | 162 ++++++++++++++++++++++++----------------
>>>>  2 files changed, 105 insertions(+), 67 deletions(-)
>>>>
>>>
>>> [...]
>>>
>>>> +static void cleanup_return_instances(struct uprobe_task *utask, bool chained,
>>>> +                                    struct pt_regs *regs)
>>>> +{
>>>> +       struct return_frame *frame = &utask->frame;
>>>> +       struct return_instance *ri = frame->return_instance;
>>>> +       enum rp_check ctx = chained ? RP_CHECK_CHAIN_CALL : RP_CHECK_CALL;
>>>> +
>>>> +       while (ri && !arch_uretprobe_is_alive(ri, ctx, regs)) {
>>>> +               ri = next_ret_instance(frame, ri);
>>>> +               utask->depth--;
>>>> +       }
>>>> +       frame->return_instance = ri;
>>>> +}
>>>> +
>>>> +static struct return_instance *alloc_return_instance(struct uprobe_task *task)
>>>> +{
>>>> +       struct return_frame *frame = &task->frame;
>>>> +
>>>> +       if (!frame->vaddr) {
>>>> +               frame->vaddr = kcalloc(MAX_URETPROBE_DEPTH,
>>>> +                               sizeof(struct return_instance), GFP_KERNEL);
>>>
>>> Are you just pre-allocating MAX_URETPROBE_DEPTH instances always?
>>> I.e., even if we need just one (because there is no recursion), you'd
>>> still waste memory for all 64 ones?
>>
>> This is the truth. On my testing machines, each struct return_instance data
>> is 28 bytes, resulting in a total pre-allocated 1792 bytes when the first
>> instrumented function is hit.
>>
>>>
>>> That seems rather wasteful.
>>>
>>> Have you considered using objpool for fast reuse across multiple CPUs?
>>> Check lib/objpool.c.
>>
>> After studying how kretprobe uses objpool, I'm convinced it is a right solution for
>> managing return_instance in uretporbe. While I need some time to fully understand
>> the objpool code itself and run some benchmark to verify its performance.
>>
>> Thanks for the suggestion.
> 
> Keep in mind that there are two patch sets under development/review,
> both of which touch this code. [0] will make return_instance
> variable-sized, so think how to accommodate that. And [1] in general
> touches a bunch of this code. So I'd let those two settle and land
> before optimizing return_instance allocations further.
> 
>   [0] https://lore.kernel.org/linux-trace-kernel/20240701164115.723677-1-jolsa@xxxxxxxxxx/
>   [1] https://lore.kernel.org/linux-kernel/20240708091241.544262971@xxxxxxxxxxxxx/

Thanks for letting me know. I've made a note to track the progress of these patch sets.

> 
>>
>>>
>>>> +               if (!frame->vaddr)
>>>> +                       return NULL;
>>>> +       }
>>>> +
>>>> +       if (!frame->return_instance) {
>>>> +               frame->return_instance = frame->vaddr;
>>>> +               return frame->return_instance;
>>>> +       }
>>>> +
>>>> +       return ++frame->return_instance;
>>>> +}
>>>> +
>>>> +static inline bool return_frame_empty(struct uprobe_task *task)
>>>> +{
>>>> +       return !task->frame.return_instance;
>>>>  }
>>>>
>>>>  /*
>>>
>>> [...]
>>
>> --
>> BR
>> Liao, Chang

-- 
BR
Liao, Chang