netdev - Re: [PATCH net-next v8 08/17] net: add helper executing custom callback from napi

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Message-ID: <20241209194447.26eaffd5@kernel.org>
Date: Mon, 9 Dec 2024 19:44:47 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: David Wei <dw@...idwei.uk>
Cc: io-uring@...r.kernel.org, netdev@...r.kernel.org, Jens Axboe
 <axboe@...nel.dk>, Pavel Begunkov <asml.silence@...il.com>, Paolo Abeni
 <pabeni@...hat.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jesper Dangaard Brouer <hawk@...nel.org>, David
 Ahern <dsahern@...nel.org>, Mina Almasry <almasrymina@...gle.com>,
 Stanislav Fomichev <stfomichev@...il.com>, Joe Damato <jdamato@...tly.com>,
 Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH net-next v8 08/17] net: add helper executing custom
 callback from napi

On Wed,  4 Dec 2024 09:21:47 -0800 David Wei wrote:
> It's useful to have napi private bits and pieces like page pool's fast
> allocating cache, so that the hot allocation path doesn't have to do any
> additional synchronisation. In case of io_uring memory provider
> introduced in following patches, we keep the consumer end of the
> io_uring's refill queue private to napi as it's a hot path.
> 
> However, from time to time we need to synchronise with the napi, for
> example to add more user memory or allocate fallback buffers. Add a
> helper function napi_execute that allows to run a custom callback from
> under napi context so that it can access and modify napi protected
> parts of io_uring. It works similar to busy polling and stops napi from
> running in the meantime, so it's supposed to be a slow control path.

Let's leave this out, please. I seriously doubt this works reliably
and the bar for adding complexity to NAPI is fairly high. A commit
which doesn't even quote any perf numbers will certainly not clear it.