Re: [PATCH 0/2] abstract napi tracking strategy

[Jens Axboe <axboe@kernel.dk>]

On 8/13/24 10:44 AM, Olivier Langlois wrote:
> the actual napi tracking strategy is inducing a non-negligeable overhead.
> Everytime a multishot poll is triggered or any poll armed, if the napi is
> enabled on the ring a lookup is performed to either add a new napi id into
> the napi_list or its timeout value is updated.
> 
> For many scenarios, this is overkill as the napi id list will be pretty
> much static most of the time. To address this common scenario, a new
> abstraction has been created following the common Linux kernel idiom of
> creating an abstract interface with a struct filled with function pointers.
> 
> Creating an alternate napi tracking strategy is therefore made in 2 phases.
> 
> 1. Introduce the io_napi_tracking_ops interface
> 2. Implement a static napi tracking by defining a new io_napi_tracking_ops

I don't think we should create ops for this, unless there's a strict
need to do so. Indirect function calls aren't cheap, and the CPU side
mitigations for security issues made them worse.

You're not wrong that ops is not an uncommon idiom in the kernel, but
it's a lot less prevalent as a solution than it used to. Exactly because
of the above reasons.

-- 
Jens Axboe