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Message-ID: <313c4834-bcee-1182-7094-4feef800c312@intel.com> Date: Thu, 18 May 2023 15:26:15 +0200 From: Alexander Lobakin <aleksander.lobakin@...el.com> To: Christoph Hellwig <hch@....de> CC: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Magnus Karlsson <magnus.karlsson@...el.com>, Michal Kubiak <michal.kubiak@...el.com>, Larysa Zaremba <larysa.zaremba@...el.com>, "Jesper Dangaard Brouer" <hawk@...nel.org>, Ilias Apalodimas <ilias.apalodimas@...aro.org>, <netdev@...r.kernel.org>, <intel-wired-lan@...ts.osuosl.org>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH net-next 06/11] net: page_pool: avoid calling no-op externals when possible From: Christoph Hellwig <hch@....de> Date: Wed, 17 May 2023 10:14:58 +0200 > So while this looks ok, Eric Dumazet had looked into some optimization > for this touching the core code, and promised me to come up with an > even better version a while ago. Eric, what's the state of your > optimizations for no-op DMA syncs? > Hmm, his last proposals were for avoiding indirect calls when IOMMU is on, but in fact we don't need to synchronize stuff -- DMA IOMMU on x86_64 also usually doesn't synchronize anything, but you don't know that prior to doing an indirect call and dma_need_sync() won't help. I was thinking of adding .dma_need_sync() callback to DMA ops, which could also be called once only on page allocation, like in this patch. Also want to hear how it goes for Eric :) Thanks, Olek
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