Re: [PATCH net-next v3 3/7] iommu/dma: avoid expensive indirect calls for sync operations
From: Robin Murphy
Date: Wed Feb 14 2024 - 13:05:22 EST
On 2024-02-14 4:21 pm, Alexander Lobakin wrote:
When IOMMU is on, the actual synchronization happens in the same cases
as with the direct DMA. Advertise %DMA_F_CAN_SKIP_SYNC in IOMMU DMA to
skip sync ops calls (indirect) for non-SWIOTLB buffers.
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
iavf yields +10% of Mpps on Rx. This also unblocks batched allocations
of XSk buffers when IOMMU is active.
Acked-by: Robin Murphy <robin.murphy@xxxxxxx>
Co-developed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
---
drivers/iommu/dma-iommu.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 50ccc4f1ef81..4ab9ac13d362 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1707,7 +1707,8 @@ static size_t iommu_dma_opt_mapping_size(void)
}
static const struct dma_map_ops iommu_dma_ops = {
- .flags = DMA_F_PCI_P2PDMA_SUPPORTED,
+ .flags = DMA_F_PCI_P2PDMA_SUPPORTED |
+ DMA_F_CAN_SKIP_SYNC,
.alloc = iommu_dma_alloc,
.free = iommu_dma_free,
.alloc_pages = dma_common_alloc_pages,