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Message-ID: <f7a082ae-5ec8-484b-b602-559f6104c9d7@intel.com> Date: Thu, 18 May 2023 15:34:44 +0200 From: Alexander Lobakin <aleksander.lobakin@...el.com> To: Jakub Kicinski <kuba@...nel.org> CC: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 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>, Christoph Hellwig <hch@....de>, <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: Jakub Kicinski <kuba@...nel.org> Date: Wed, 17 May 2023 21:08:04 -0700 > On Tue, 16 May 2023 18:18:36 +0200 Alexander Lobakin wrote: >> + /* Try to avoid calling no-op syncs */ >> + pool->p.flags |= PP_FLAG_DMA_MAYBE_SYNC; >> + pool->p.flags &= ~PP_FLAG_DMA_SYNC_DEV; >> } >> >> if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT && >> @@ -323,6 +327,12 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page) >> >> page_pool_set_dma_addr(page, dma); >> >> + if ((pool->p.flags & PP_FLAG_DMA_MAYBE_SYNC) && >> + dma_need_sync(pool->p.dev, dma)) { >> + pool->p.flags |= PP_FLAG_DMA_SYNC_DEV; >> + pool->p.flags &= ~PP_FLAG_DMA_MAYBE_SYNC; >> + } > > is it just me or does it feel cleaner to allocate a page at init, > and throw it into the cache, rather than adding a condition to a > fast(ish) path? When recycling is on, not that fast -- new allocations occur relatively rarely and it's allocations anyway, one `if` doesn't change anything there. And seems like I didn't get the sentence regarding "allocate and throw" :s This condition just disables the shortcut if any new page suddenly requires real DMA syncs (and if it does, then the sync a line below will take way more time than 1 more `if` anyway). Thanks, Olek
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