Hi VPP maintainers,
Recently VPP has upgraded the DPDK version to DPDK-21.08, which includes two
optimization patches[1][2] from Arm DPDK team. With the mbuf-fast-free flag,
the two patches add code segment to accelerate mbuf free in PMD TX path for
i40e driver, which shows quite obvious performance improvement from DPDK L3FWD
benchmarking results.
I tried to verify the benefits that those optimization patches can bring up to
VPP, but find out that mbuf-fast-free flag is not enabled in VPP+DPDK by
default.
Applying DPDK mbuf-fast-free has some constraints, e.g,
* mbufs to be freed should be coming from the same mempool
* ref_cnt == 1 always in mbuf meta-data when user apps call DPDK
rte_eth_tx_burst ()
* No TX checksum offload
* No jumble frame
But VPP vector mode(set by adding ‘no-tx-checksum-offload’ and ‘no-multi-seg’
parameters in dpdk section of the startup.conf) seems to satisfy all the
requirements. So I made a few code changes shown as below to set mbuf-fast-free
flag by default in VPP vector mode and did some benchmarking for IPv4 routing
test cases with 1 flow/10k flows. The benchmarking results show both throughput
improvement and CPU cycles saved regarding DPDK transmit function.
So any thought on enabling mbuf-fast-free tx offload flag in VPP vector mode?
Any feedback is welcome :)
Code Changes:
diff --git a/src/plugins/dpdk/device/init.c b/src/plugins/dpdk/device/init.c
index f7c1cc106..0fbdd2317 100644
--- a/src/plugins/dpdk/device/init.c
+++ b/src/plugins/dpdk/device/init.c
@@ -398,6 +398,8 @@ dpdk_lib_init (dpdk_main_t * dm)
xd->port_conf.rxmode.offloads |= DEV_RX_OFFLOAD_SCATTER;
xd->flags |= DPDK_DEVICE_FLAG_MAYBE_MULTISEG;
}
+ if (dm->conf->no_multi_seg && dm->conf->no_tx_checksum_offload)
+ xd->port_conf.txmode.offloads |= DEV_TX_OFFLOAD_MBUF_FAST_FREE;
xd->tx_q_used = clib_min (dev_info.max_tx_queues, tm->n_vlib_mains);
Benchmark Results:
1 flow, bidirectional
Throughput(Mpps):
Original
Patched
Ratio
N1SDP
11.62
12.44
+7.06%
ThunderX2
9.52
10.16
+6.30%
Dell 8268
17.82
18.20
+2.13%
CPU cycles overhead for DPDK transmit function(recorded by Perf tools):
Original
Patched
Ratio
N1SDP
13.08%
5.53%
-7.55%
ThunderX2
11.01%
6.68%
-4.33%
Dell 8268
10.78%
7.35%
-3.43%
10k flows, bidirectional
Throughput(Mpps):
Original
Patched
Ratio
N1SDP
8.48
9.0
+6.13%
ThunderX2
8.84
9.26
+4.75%
Dell 8268
15.04
15.40
+2.39%
CPU cycles overhead for DPDK transmit function(recorded by Perf tools):
Original
Patched
Ratio
N1SDP
10.58%
4.54%
-6.04%
ThunderX2
12.92%
6.63%
-6.29%
Dell 8268
10.36%
7.97%
-2.39%
[1]
http://git.dpdk.org/dpdk/commit/?h=v21.08-rc1&id=be8ff6210851fdacbe00033259b7dc5426e95589
[2]
http://git.dpdk.org/dpdk/commit/?h=v21.08-rc1&id=95e7bb6a5fc9e371e763b11ec15786e4d574ef8e
Best Regards,
Jieqiang Wang
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