[apparmor] use per-cpu refcounts for apparmor labels?

[John Johansen]

On 9/25/23 16:49, Vinicius Costa Gomes wrote:
> Hi Mateusz,
> 
> Mateusz Guzik <mjguzik at gmail.com> writes:
> 
>> I'm sanity-checking perf in various microbenchmarks and I found
>> apparmor to be the main bottleneck in some of them.
>>
>> For example: will-it-scale open1_processes -t 16, top of the profile:
>>    20.17%  [kernel]                   [k] apparmor_file_alloc_security
>>    20.08%  [kernel]                   [k] apparmor_file_open
>>    20.05%  [kernel]                   [k] apparmor_file_free_security
>>    18.39%  [kernel]                   [k] apparmor_current_getsecid_subj
>> [snip]
>>
>> This serializes on refing/unrefing apparmor objs, sounds like a great
>> candidate for per-cpu refcounting instead (I'm assuming they are
>> expected to be long-lived).
>>
>> I would hack it up myself, but I failed to find a clear spot to switch
>> back from per-cpu to centalized operation and don't want to put
>> serious effort into it.
>>
>> Can you sort this out?
> 

I will add looking into it on the todo list. Its going to have to come
after some other major cleanups land, and I am not sure we can make
the semantic work well for some of these. For other we might get away
with switching to a critical section like Vinicius's patch has done
for apparmor_current_getsecid_subj.

> I was looking at this same workload, and proposed a patch[1] some time
> ago, see if it helps:
> 
> https://lists.ubuntu.com/archives/apparmor/2023-August/012914.html
> 
> But my idea was different, in many cases, we are looking at the label
> associated with the current task, and there's no need to take the
> refcount.
> 

yes, and thanks for that.

>>
>> Thanks,
>> -- 
>> Mateusz Guzik <mjguzik gmail.com>
>>
> 
> Cheers,