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Date: Wed, 1 Oct 2014 23:00:42 -0700
From: Alexei Starovoitov <ast@...mgrid.com>
To: "David S. Miller" <davem@...emloft.net>
Cc: Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
Alexander Duyck <alexander.h.duyck@...el.com>,
Ben Hutchings <ben@...adent.org.uk>,
Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org
Subject: RFC: ixgbe+build_skb+extra performance experiments
Hi All,
I'm trying to speed up single core packet per second.
I took dual port ixgbe and added both ports to a linux bridge.
Only one port is connected to another system running pktgen at 10G rate.
I disabled gro to measure pure RX speed of ixgbe.
Out of the box I see 6.5 Mpps and the following stack:
21.83% ksoftirqd/0 [kernel.kallsyms] [k] memcpy
17.58% ksoftirqd/0 [ixgbe] [k] ixgbe_clean_rx_irq
10.07% ksoftirqd/0 [kernel.kallsyms] [k] build_skb
6.40% ksoftirqd/0 [kernel.kallsyms] [k] __netdev_alloc_frag
5.18% ksoftirqd/0 [kernel.kallsyms] [k] put_compound_page
4.93% ksoftirqd/0 [kernel.kallsyms] [k] kmem_cache_alloc
4.55% ksoftirqd/0 [kernel.kallsyms] [k] __netif_receive_skb_core
Obviously driver spends huge amount of time copying data from
hw buffers into skb.
Then I applied buggy but working in this case patch:
http://patchwork.ozlabs.org/patch/236044/
that is trying to use build_skb() API in ixgbe.
RX speed jumped to 7.6 Mpps with the following stack:
27.02% ksoftirqd/0 [kernel.kallsyms] [k] eth_type_trans
16.68% ksoftirqd/0 [ixgbe] [k] ixgbe_clean_rx_irq
11.45% ksoftirqd/0 [kernel.kallsyms] [k] build_skb
5.20% ksoftirqd/0 [kernel.kallsyms] [k] __netif_receive_skb_core
4.72% ksoftirqd/0 [kernel.kallsyms] [k] kmem_cache_alloc
3.96% ksoftirqd/0 [kernel.kallsyms] [k] kmem_cache_free
packets no longer copied and performance is higher.
It's doing the following:
- build_skb out of hw buffer and prefetch packet data
- eth_type_trans
- napi_gro_receive
but build_skb() is too fast and cpu doesn't have enough time
to prefetch packet data before eth_type_trans() is called,
so I added mini skb bursting of 2 skbs (patch below) that does:
- build_skb1 out of hw buffer and prefetch packet data
- build_skb2 out of hw buffer and prefetch packet data
- eth_type_trans(skb1)
- napi_gro_receive(skb1)
- eth_type_trans(skb2)
- napi_gro_receive(skb2)
and performance jumped to 9.0 Mpps with stack:
20.54% ksoftirqd/0 [ixgbe] [k] ixgbe_clean_rx_irq
13.15% ksoftirqd/0 [kernel.kallsyms] [k] build_skb
8.35% ksoftirqd/0 [kernel.kallsyms] [k] __netif_receive_skb_core
7.16% ksoftirqd/0 [kernel.kallsyms] [k] eth_type_trans
4.73% ksoftirqd/0 [kernel.kallsyms] [k] kmem_cache_free
4.50% ksoftirqd/0 [kernel.kallsyms] [k] kmem_cache_alloc
with further instruction tunning inside ixgbe_clean_rx_irq()
I could push it to 9.4 Mpps.
>From 6.5 Mpps to 9.4 Mpps via build_skb() and tunning.
Is there a way to fix the issue Ben pointed a year ago?
Brute force fix could to be: avoid half-page buffers.
We'll be wasting 16Mbyte of memory. Sure, but in some cases
extra peformance might be worth it.
Other options?
I think we need to try harder to switch to build_skb()
It will open up a lot of possibilities for further performance
improvements.
Thoughts?
---
drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 34 +++++++++++++++++++++----
1 file changed, 29 insertions(+), 5 deletions(-)
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 21d1a65..1d1e37f 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -1590,8 +1590,6 @@ static void ixgbe_process_skb_fields(struct ixgbe_ring *rx_ring,
}
skb_record_rx_queue(skb, rx_ring->queue_index);
-
- skb->protocol = eth_type_trans(skb, dev);
}
static void ixgbe_rx_skb(struct ixgbe_q_vector *q_vector,
@@ -2063,6 +2061,24 @@ dma_sync:
return skb;
}
+#define BURST_SIZE 2
+static void ixgbe_rx_skb_burst(struct sk_buff *skbs[BURST_SIZE],
+ unsigned int skb_burst,
+ struct ixgbe_q_vector *q_vector,
+ struct net_device *dev)
+{
+ int i;
+
+ for (i = 0; i < skb_burst; i++) {
+ struct sk_buff *skb = skbs[i];
+
+ skb->protocol = eth_type_trans(skb, dev);
+
+ skb_mark_napi_id(skb, &q_vector->napi);
+ ixgbe_rx_skb(q_vector, skb);
+ }
+}
+
/**
* ixgbe_clean_rx_irq - Clean completed descriptors from Rx ring - bounce buf
* @q_vector: structure containing interrupt and ring information
@@ -2087,6 +2103,8 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
unsigned int mss = 0;
#endif /* IXGBE_FCOE */
u16 cleaned_count = ixgbe_desc_unused(rx_ring);
+ struct sk_buff *skbs[BURST_SIZE];
+ unsigned int skb_burst = 0;
while (likely(total_rx_packets < budget)) {
union ixgbe_adv_rx_desc *rx_desc;
@@ -2161,13 +2179,19 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
}
#endif /* IXGBE_FCOE */
- skb_mark_napi_id(skb, &q_vector->napi);
- ixgbe_rx_skb(q_vector, skb);
-
/* update budget accounting */
total_rx_packets++;
+ skbs[skb_burst++] = skb;
+
+ if (skb_burst == BURST_SIZE) {
+ ixgbe_rx_skb_burst(skbs, skb_burst, q_vector,
+ rx_ring->netdev);
+ skb_burst = 0;
+ }
}
+ ixgbe_rx_skb_burst(skbs, skb_burst, q_vector, rx_ring->netdev);
+
u64_stats_update_begin(&rx_ring->syncp);
rx_ring->stats.packets += total_rx_packets;
rx_ring->stats.bytes += total_rx_bytes;
--
1.7.9.5
--
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