Messages in this thread Patch in this message | | | From | Alexander Lobakin <> | Subject | [PATCH net-next 6/9] page_pool: avoid calling no-op externals when possible | Date | Thu, 27 Jul 2023 16:43:33 +0200 |
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Turned out page_pool_put{,_full}_page() can burn quite a bunch of cycles even when on DMA-coherent platforms (like x86) with no active IOMMU or swiotlb, just for the call ladder. Indeed, it's
page_pool_put_page() page_pool_put_defragged_page() <- external __page_pool_put_page() page_pool_dma_sync_for_device() <- non-inline dma_sync_single_range_for_device() dma_sync_single_for_device() <- external dma_direct_sync_single_for_device() dev_is_dma_coherent() <- exit
For the inline functions, no guarantees the compiler won't uninline them (they're clearly not one-liners and sometimes compilers uninline even 2 + 2). The first external call is necessary, but the rest 2+ are done for nothing each time, plus a bunch of checks here and there. Since Page Pool mappings are long-term and for one "device + addr" pair dma_need_sync() will always return the same value (basically, whether it belongs to an swiotlb pool), addresses can be tested once right after they're obtained and the result can be reused until the page is unmapped. Define the new PP DMA sync operation type, which will mean "do DMA syncs for the device, but only when needed" and turn it on by default when the driver asks to sync pages. When a page is mapped, check whether it needs syncs and if so, replace that "sync when needed" back to "always do syncs" globally for the whole pool (better safe than sorry). As long as the pool has no pages requiring DMA syncs, this cuts off a good piece of calls and checks. When at least one page required it, the pool conservatively falls back to "always call sync functions", no per-page verdicts. It's a fairly rare case anyway that only a few pages would require syncing. On my x86_64, this gives from 2% to 5% performance benefit with no negative impact for cases when IOMMU is on and the shortcut can't be used.
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com> --- include/net/page_pool/types.h | 3 ++- net/core/page_pool.c | 7 ++++++- 2 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h index dd26f4b2b66c..9134fb458cb2 100644 --- a/include/net/page_pool/types.h +++ b/include/net/page_pool/types.h @@ -97,8 +97,9 @@ struct page_pool { bool dma_map:1; /* Perform DMA mapping */ enum { PP_DMA_SYNC_ACT_DISABLED = 0, /* Driver didn't ask to sync */ + PP_DMA_SYNC_ACT_SKIP, /* Syncs can be skipped */ PP_DMA_SYNC_ACT_DO, /* Perform DMA sync ops */ - } dma_sync_act:1; + } dma_sync_act:2; bool page_frag:1; /* Allow page fragments */ long frag_users; diff --git a/net/core/page_pool.c b/net/core/page_pool.c index 6a8f105e2df5..529e4b41e9eb 100644 --- a/net/core/page_pool.c +++ b/net/core/page_pool.c @@ -197,7 +197,8 @@ static int page_pool_init(struct page_pool *pool, if (!pool->p.max_len) return -EINVAL; - pool->dma_sync_act = PP_DMA_SYNC_ACT_DO; + /* Try to avoid calling no-op syncs */ + pool->dma_sync_act = PP_DMA_SYNC_ACT_SKIP; /* pool->p.offset has to be set according to the address * offset used by the DMA engine to start copying rx data @@ -350,6 +351,10 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page) page_pool_set_dma_addr(page, dma); + if (pool->dma_sync_act == PP_DMA_SYNC_ACT_SKIP && + dma_need_sync(pool->p.dev, dma)) + pool->dma_sync_act = PP_DMA_SYNC_ACT_DO; + if (pool->dma_sync_act == PP_DMA_SYNC_ACT_DO) page_pool_dma_sync_for_device(pool, page, pool->p.max_len); -- 2.41.0
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