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Message-ID: <3da1da0972c6c6af1fd4db2e4227043fab78e37f.camel@nvidia.com> Date: Wed, 5 Apr 2023 17:04:43 +0000 From: Dragos Tatulea <dtatulea@...dia.com> To: "kuba@...nel.org" <kuba@...nel.org> CC: "hawk@...nel.org" <hawk@...nel.org>, Tariq Toukan <tariqt@...dia.com>, "edumazet@...gle.com" <edumazet@...gle.com>, "davem@...emloft.net" <davem@...emloft.net>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "pabeni@...hat.com" <pabeni@...hat.com>, "ilias.apalodimas@...aro.org" <ilias.apalodimas@...aro.org> Subject: Re: [RFC net-next 1/2] page_pool: allow caching from safely localized NAPI On Mon, 2023-04-03 at 10:12 -0700, Jakub Kicinski wrote: > On Mon, 3 Apr 2023 18:30:55 +0300 Ilias Apalodimas wrote: > > > Meaning in page_pool_return_skb_page() or all the way from > > > napi_consume_skb()? The former does indeed sounds like a good > > > idea! > > > > page_pool_return_skb_page() (and maybe page_pool_put_full_page()). > > FWIW we completely agree on napi_consume_skb(). We are trying to > > keep > > page_pool and the net layer as disjoint as possible. The only > > point > > we 'pollute' networking code is the recycle bit checking and we'd > > prefer keeping it like that > > Ack, OTOH plumbing thru the budget argument within netdev code should > not be a major refactoring. So maybe I should do that after all. > > Otherwise we have two different conditions - netdev only recycles > skbs > based on the NAPI budget != 0, but page pool will assume that > in_softirq() && !in_hardirq() is always safe. > > The latter is safe, I think, unless someone adds a print half way > thru > the cache update... but then it's also safe in NAPI skb recycling, > so napi_consume_skb() should stop taking the budget and just look > at preempt flags... > > To make the correctness obvious, for now, I think I will refactor > the netdev code to pass a "in NAPI poll" bool to > page_pool_return_skb_page(), and add a WARN_ON(!softirq || hardirq). > > Let's see how the code ends up looking, I'll send it as RFCv2 rather > than PATCH to make it clear I'm not sure it's okay with you :) Wow, thanks for picking this up so fast! After enabling this in the mlx5 driver, there is already improved page_pool cache usage for our test with the application running on the same CPU with the receive queue NAPI (0 -> 98 % cache usage). Looking forward to the v2.
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