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Date: Tue, 15 Nov 2022 18:28:41 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: Joerg Roedel <joro@...tes.org>,
Robin Murphy <robin.murphy@....com>,
Will Deacon <will@...nel.org>
Cc: linux-kernel <linux-kernel@...r.kernel.org>,
netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
Eric Dumazet <eric.dumazet@...il.com>, iommu@...ts.linux.dev
Subject: [PATCH v2 -next] iommu/dma: avoid expensive indirect calls for sync operations
Quite often, NIC 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, as shown in [1]
Even if/when CONFIG_RETPOLINE is not set, there
is a cost of about 3%.
This patch adds dev->skip_dma_sync boolean that can be opted-in.
For instance iommu_setup_dma_ops() can set this boolean to true
if CONFIG_DMA_API_DEBUG is not set, and dev_is_dma_coherent(dev).
Then later, if/when swiotlb is used for the first time, the flag
is turned off, from swiotlb_tbl_map_single()
We might in the future inline again these helpers, like:
static void inline
dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
size_t size, enum dma_data_direction dir)
{
if (!dev_skip_dma_sync(dev))
__dma_sync_single_for_cpu(dev, addr, size, dir);
}
perf profile before the patch:
18.53% [kernel] [k] gq_rx_skb
14.77% [kernel] [k] napi_reuse_skb
8.95% [kernel] [k] skb_release_data
5.42% [kernel] [k] dev_gro_receive
5.37% [kernel] [k] memcpy
<*> 5.26% [kernel] [k] iommu_dma_sync_sg_for_cpu
4.78% [kernel] [k] tcp_gro_receive
<*> 4.42% [kernel] [k] iommu_dma_sync_sg_for_device
4.12% [kernel] [k] ipv6_gro_receive
3.65% [kernel] [k] gq_pool_get
3.25% [kernel] [k] skb_gro_receive
2.07% [kernel] [k] napi_gro_frags
1.98% [kernel] [k] tcp6_gro_receive
1.27% [kernel] [k] gq_rx_prep_buffers
1.18% [kernel] [k] gq_rx_napi_handler
0.99% [kernel] [k] csum_partial
0.74% [kernel] [k] csum_ipv6_magic
0.72% [kernel] [k] free_pcp_prepare
0.60% [kernel] [k] __napi_poll
0.58% [kernel] [k] net_rx_action
0.56% [kernel] [k] read_tsc
<*> 0.50% [kernel] [k] __x86_indirect_thunk_r11
0.45% [kernel] [k] memset
After patch, lines with <*> no longer show up, and overall
cpu usage looks much better (~60% instead of ~72%)
25.56% [kernel] [k] gq_rx_skb
9.90% [kernel] [k] napi_reuse_skb
7.39% [kernel] [k] dev_gro_receive
6.78% [kernel] [k] memcpy
6.53% [kernel] [k] skb_release_data
6.39% [kernel] [k] tcp_gro_receive
5.71% [kernel] [k] ipv6_gro_receive
4.35% [kernel] [k] napi_gro_frags
4.34% [kernel] [k] skb_gro_receive
3.50% [kernel] [k] gq_pool_get
3.08% [kernel] [k] gq_rx_napi_handler
2.35% [kernel] [k] tcp6_gro_receive
2.06% [kernel] [k] gq_rx_prep_buffers
1.32% [kernel] [k] csum_partial
0.93% [kernel] [k] csum_ipv6_magic
0.65% [kernel] [k] net_rx_action
Many thanks to Robin Murphy for his feedback and ideas to make this patch
much better !
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Robin Murphy <robin.murphy@....com>
Cc: Joerg Roedel <joro@...tes.org>
Cc: Will Deacon <will@...nel.org>
Cc: iommu@...ts.linux.dev
---
drivers/iommu/dma-iommu.c | 2 ++
include/linux/device.h | 1 +
include/linux/dma-map-ops.h | 5 +++++
kernel/dma/mapping.c | 20 ++++++++++++++++----
kernel/dma/swiotlb.c | 3 +++
5 files changed, 27 insertions(+), 4 deletions(-)
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 9297b741f5e80e2408e864fc3f779410d6b04d49..bd3f4d3d646cc57c7588f22d49ea32ac693e38ff 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1587,6 +1587,8 @@ void iommu_setup_dma_ops(struct device *dev, u64 dma_base, u64 dma_limit)
if (iommu_dma_init_domain(domain, dma_base, dma_limit, dev))
goto out_err;
dev->dma_ops = &iommu_dma_ops;
+ if (!IS_ENABLED(CONFIG_DMA_API_DEBUG) && dev_is_dma_coherent(dev))
+ dev->skip_dma_sync = true;
}
return;
diff --git a/include/linux/device.h b/include/linux/device.h
index 424b55df02727b5742070f72374fd65f5dd68151..2fbb2cc18e44e21eba5f43557ee16d0dc92ef2ef 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -647,6 +647,7 @@ struct device {
defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
bool dma_coherent:1;
#endif
+ bool skip_dma_sync:1;
#ifdef CONFIG_DMA_OPS_BYPASS
bool dma_ops_bypass : 1;
#endif
diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index d678afeb8a13a3a54380a959d14f79bca9c23d8e..4691081f71c51da5468cf6703570ebc7a64d40c5 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -275,6 +275,11 @@ static inline bool dev_is_dma_coherent(struct device *dev)
}
#endif /* CONFIG_ARCH_HAS_DMA_COHERENCE_H */
+static inline bool dev_skip_dma_sync(struct device *dev)
+{
+ return dev->skip_dma_sync;
+}
+
void *arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
gfp_t gfp, unsigned long attrs);
void arch_dma_free(struct device *dev, size_t size, void *cpu_addr,
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 33437d6206445812b6d4d5b33c77235d18074dec..5d5d286ffae7fa6b7ff1aef46bdc59e7e31a8038 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -328,9 +328,12 @@ EXPORT_SYMBOL(dma_unmap_resource);
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);
+ const struct dma_map_ops *ops;
BUG_ON(!valid_dma_direction(dir));
+ if (dev_skip_dma_sync(dev))
+ return;
+ ops = get_dma_ops(dev);;
if (dma_map_direct(dev, ops))
dma_direct_sync_single_for_cpu(dev, addr, size, dir);
else if (ops->sync_single_for_cpu)
@@ -342,9 +345,12 @@ EXPORT_SYMBOL(dma_sync_single_for_cpu);
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);
+ const struct dma_map_ops *ops;
BUG_ON(!valid_dma_direction(dir));
+ if (dev_skip_dma_sync(dev))
+ return;
+ ops = get_dma_ops(dev);;
if (dma_map_direct(dev, ops))
dma_direct_sync_single_for_device(dev, addr, size, dir);
else if (ops->sync_single_for_device)
@@ -356,9 +362,12 @@ EXPORT_SYMBOL(dma_sync_single_for_device);
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);
+ const struct dma_map_ops *ops;
BUG_ON(!valid_dma_direction(dir));
+ if (dev_skip_dma_sync(dev))
+ return;
+ ops = get_dma_ops(dev);;
if (dma_map_direct(dev, ops))
dma_direct_sync_sg_for_cpu(dev, sg, nelems, dir);
else if (ops->sync_sg_for_cpu)
@@ -370,9 +379,12 @@ EXPORT_SYMBOL(dma_sync_sg_for_cpu);
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);
+ const struct dma_map_ops *ops;
BUG_ON(!valid_dma_direction(dir));
+ if (dev_skip_dma_sync(dev))
+ return;
+ ops = get_dma_ops(dev);;
if (dma_map_direct(dev, ops))
dma_direct_sync_sg_for_device(dev, sg, nelems, dir);
else if (ops->sync_sg_for_device)
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 339a990554e7fed98dd337efe4fb759a98161cdb..03ebd9803db1a457600f1fac8a18fb3dde724a6f 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -734,6 +734,9 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr,
int index;
phys_addr_t tlb_addr;
+ if (unlikely(dev->skip_dma_sync))
+ dev->skip_dma_sync = false;
+
if (!mem || !mem->nslabs) {
dev_warn_ratelimited(dev,
"Can not allocate SWIOTLB buffer earlier and can't now provide you with the DMA bounce buffer");
--
2.38.1.431.g37b22c650d-goog
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