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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Alexander Lobakin , Christoph Hellwig , Marek Szyprowski , Robin Murphy , Joerg Roedel , Will Deacon , "Rafael J. Wysocki" , Magnus Karlsson , nex.sw.ncis.osdt.itp.upstreaming@intel.com, bpf@vger.kernel.org, netdev@vger.kernel.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org Subject: [PATCH net-next v4 2/7] dma: avoid redundant calls for sync operations Date: Tue, 23 Apr 2024 15:58:27 +0200 Message-ID: <20240423135832.2271696-3-aleksander.lobakin@intel.com> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240423135832.2271696-1-aleksander.lobakin@intel.com> References: <20240423135832.2271696-1-aleksander.lobakin@intel.com> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Quite often, devices do not need dma_sync operations on x86_64 at least. Indeed, when dev_is_dma_coherent(dev) is true and dev_use_swiotlb(dev) is false, iommu_dma_sync_single_for_cpu() and friends do nothing. However, indirectly calling them when CONFIG_RETPOLINE=y consumes about 10% of cycles on a cpu receiving packets from softirq at ~100Gbit rate. Even if/when CONFIG_RETPOLINE is not set, there is a cost of about 3%. Add dev->need_dma_sync boolean and turn it off during the device initialization (dma_set_mask()) depending on the setup: dev_is_dma_coherent() for the direct DMA, !(sync_single_for_device || sync_single_for_cpu) or the new dma_map_ops flag, %DMA_F_CAN_SKIP_SYNC, advertised for non-NULL DMA ops. Then later, if/when swiotlb is used for the first time, the flag is reset back to on, from swiotlb_tbl_map_single(). On iavf, the UDP trafficgen with XDP_DROP in skb mode test shows +3-5% increase for direct DMA. Suggested-by: Christoph Hellwig # direct DMA shortcut Co-developed-by: Eric Dumazet Signed-off-by: Eric Dumazet Signed-off-by: Alexander Lobakin --- include/linux/device.h | 4 +++ include/linux/dma-map-ops.h | 12 ++++++++ include/linux/dma-mapping.h | 53 +++++++++++++++++++++++++++++++---- kernel/dma/mapping.c | 55 +++++++++++++++++++++++++++++-------- kernel/dma/swiotlb.c | 6 ++++ 5 files changed, 113 insertions(+), 17 deletions(-) diff --git a/include/linux/device.h b/include/linux/device.h index b9f5464f44ed..ed95b829f05b 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -691,6 +691,7 @@ struct device_physical_location { * and optionall (if the coherent mask is large enough) also * for dma allocations. This flag is managed by the dma ops * instance from ->dma_supported. + * @dma_need_sync: The device needs performing DMA sync operations. * * At the lowest level, every device in a Linux system is represented by an * instance of struct device. The device structure contains the information @@ -803,6 +804,9 @@ struct device { #ifdef CONFIG_DMA_OPS_BYPASS bool dma_ops_bypass : 1; #endif +#ifdef CONFIG_DMA_NEED_SYNC + bool dma_need_sync:1; +#endif }; /** diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h index 4abc60f04209..4893cb89cb52 100644 --- a/include/linux/dma-map-ops.h +++ b/include/linux/dma-map-ops.h @@ -18,8 +18,11 @@ struct iommu_ops; * * DMA_F_PCI_P2PDMA_SUPPORTED: Indicates the dma_map_ops implementation can * handle PCI P2PDMA pages in the map_sg/unmap_sg operation. + * DMA_F_CAN_SKIP_SYNC: DMA sync operations can be skipped if the device is + * coherent and it's not an SWIOTLB buffer. */ #define DMA_F_PCI_P2PDMA_SUPPORTED (1 << 0) +#define DMA_F_CAN_SKIP_SYNC (1 << 1) struct dma_map_ops { unsigned int flags; @@ -273,6 +276,15 @@ static inline bool dev_is_dma_coherent(struct device *dev) } #endif /* CONFIG_ARCH_HAS_DMA_COHERENCE_H */ +static inline void dma_reset_need_sync(struct device *dev) +{ +#ifdef CONFIG_DMA_NEED_SYNC + /* Reset it only once so that the function can be called on hotpath */ + if (unlikely(!dev->dma_need_sync)) + dev->dma_need_sync = true; +#endif +} + /* * Check whether potential kmalloc() buffers are safe for non-coherent DMA. */ diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index a569b56b25e2..eb4e15893b6c 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -282,16 +282,59 @@ static inline int dma_mmap_noncontiguous(struct device *dev, #endif /* CONFIG_HAS_DMA */ #if defined(CONFIG_HAS_DMA) && defined(CONFIG_DMA_NEED_SYNC) -void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size, +void __dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size, enum dma_data_direction dir); -void dma_sync_single_for_device(struct device *dev, dma_addr_t addr, +void __dma_sync_single_for_device(struct device *dev, dma_addr_t addr, size_t size, enum dma_data_direction dir); -void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, +void __dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nelems, enum dma_data_direction dir); -void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, +void __dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, int nelems, enum dma_data_direction dir); -bool dma_need_sync(struct device *dev, dma_addr_t dma_addr); +bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr); + +static inline bool dma_dev_need_sync(const struct device *dev) +{ + /* Always call DMA sync operations when debugging is enabled */ + return dev->dma_need_sync || IS_ENABLED(CONFIG_DMA_API_DEBUG); +} + +static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, + size_t size, enum dma_data_direction dir) +{ + if (dma_dev_need_sync(dev)) + __dma_sync_single_for_cpu(dev, addr, size, dir); +} + +static inline void dma_sync_single_for_device(struct device *dev, + dma_addr_t addr, size_t size, enum dma_data_direction dir) +{ + if (dma_dev_need_sync(dev)) + __dma_sync_single_for_device(dev, addr, size, dir); +} + +static inline void dma_sync_sg_for_cpu(struct device *dev, + struct scatterlist *sg, int nelems, enum dma_data_direction dir) +{ + if (dma_dev_need_sync(dev)) + __dma_sync_sg_for_cpu(dev, sg, nelems, dir); +} + +static inline void dma_sync_sg_for_device(struct device *dev, + struct scatterlist *sg, int nelems, enum dma_data_direction dir) +{ + if (dma_dev_need_sync(dev)) + __dma_sync_sg_for_device(dev, sg, nelems, dir); +} + +static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr) +{ + return dma_dev_need_sync(dev) ? __dma_need_sync(dev, dma_addr) : false; +} #else /* !CONFIG_HAS_DMA || !CONFIG_DMA_NEED_SYNC */ +static inline bool dma_dev_need_sync(const struct device *dev) +{ + return false; +} static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size, enum dma_data_direction dir) { diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c index c78b78e95a26..3524bc92c37f 100644 --- a/kernel/dma/mapping.c +++ b/kernel/dma/mapping.c @@ -330,7 +330,7 @@ void dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size, EXPORT_SYMBOL(dma_unmap_resource); #ifdef CONFIG_DMA_NEED_SYNC -void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size, +void __dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size, enum dma_data_direction dir) { const struct dma_map_ops *ops = get_dma_ops(dev); @@ -342,9 +342,9 @@ void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size, ops->sync_single_for_cpu(dev, addr, size, dir); debug_dma_sync_single_for_cpu(dev, addr, size, dir); } -EXPORT_SYMBOL(dma_sync_single_for_cpu); +EXPORT_SYMBOL(__dma_sync_single_for_cpu); -void dma_sync_single_for_device(struct device *dev, dma_addr_t addr, +void __dma_sync_single_for_device(struct device *dev, dma_addr_t addr, size_t size, enum dma_data_direction dir) { const struct dma_map_ops *ops = get_dma_ops(dev); @@ -356,9 +356,9 @@ void dma_sync_single_for_device(struct device *dev, dma_addr_t addr, ops->sync_single_for_device(dev, addr, size, dir); debug_dma_sync_single_for_device(dev, addr, size, dir); } -EXPORT_SYMBOL(dma_sync_single_for_device); +EXPORT_SYMBOL(__dma_sync_single_for_device); -void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, +void __dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nelems, enum dma_data_direction dir) { const struct dma_map_ops *ops = get_dma_ops(dev); @@ -370,9 +370,9 @@ void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, ops->sync_sg_for_cpu(dev, sg, nelems, dir); debug_dma_sync_sg_for_cpu(dev, sg, nelems, dir); } -EXPORT_SYMBOL(dma_sync_sg_for_cpu); +EXPORT_SYMBOL(__dma_sync_sg_for_cpu); -void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, +void __dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, int nelems, enum dma_data_direction dir) { const struct dma_map_ops *ops = get_dma_ops(dev); @@ -384,18 +384,47 @@ void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, ops->sync_sg_for_device(dev, sg, nelems, dir); debug_dma_sync_sg_for_device(dev, sg, nelems, dir); } -EXPORT_SYMBOL(dma_sync_sg_for_device); +EXPORT_SYMBOL(__dma_sync_sg_for_device); -bool dma_need_sync(struct device *dev, dma_addr_t dma_addr) +bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr) { const struct dma_map_ops *ops = get_dma_ops(dev); if (dma_map_direct(dev, ops)) + /* + * dma_need_sync could've been reset on first SWIOTLB buffer + * mapping, but @dma_addr is not necessary an SWIOTLB buffer. + * In this case, fall back to more granular check. + */ return dma_direct_need_sync(dev, dma_addr); - return ops->sync_single_for_cpu || ops->sync_single_for_device; + return true; } -EXPORT_SYMBOL_GPL(dma_need_sync); -#endif /* CONFIG_DMA_NEED_SYNC */ +EXPORT_SYMBOL_GPL(__dma_need_sync); + +static void dma_setup_need_sync(struct device *dev) +{ + const struct dma_map_ops *ops = get_dma_ops(dev); + + if (dma_map_direct(dev, ops) || (ops->flags & DMA_F_CAN_SKIP_SYNC)) + /* + * dma_need_sync will be reset to %true on first SWIOTLB buffer + * mapping, if any. During the device initialization, it's + * enough to check only for the DMA coherence. + */ + dev->dma_need_sync = !dev_is_dma_coherent(dev); + else if (!ops->sync_single_for_device && !ops->sync_single_for_cpu && + !ops->sync_sg_for_device && !ops->sync_sg_for_cpu) + /* + * Synchronization is not possible when none of DMA sync ops + * is set. + */ + dev->dma_need_sync = false; + else + dev->dma_need_sync = true; +} +#else /* !CONFIG_DMA_NEED_SYNC */ +static inline void dma_setup_need_sync(struct device *dev) { } +#endif /* !CONFIG_DMA_NEED_SYNC */ /* * The whole dma_get_sgtable() idea is fundamentally unsafe - it seems @@ -785,6 +814,8 @@ int dma_set_mask(struct device *dev, u64 mask) arch_dma_set_mask(dev, mask); *dev->dma_mask = mask; + dma_setup_need_sync(dev); + return 0; } EXPORT_SYMBOL(dma_set_mask); diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index a5e0dfc44d24..3b9dddbcdda7 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -1379,6 +1379,12 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr, return (phys_addr_t)DMA_MAPPING_ERROR; } + /* + * If dma_need_sync wasn't set, reset it on first SWIOTLB buffer + * mapping to always sync SWIOTLB buffers. + */ + dma_reset_need_sync(dev); + /* * Save away the mapping from the original address to the DMA address. * This is needed when we sync the memory. Then we sync the buffer if -- 2.44.0