[PATCH 1/2 net-next] net: fec: add napi support to improve proformance
Eric Dumazet
eric.dumazet at gmail.com
Wed Jan 23 08:49:14 EST 2013
On Wed, 2013-01-23 at 15:37 +0800, Frank Li wrote:
> 2013/1/23 Eric Dumazet <eric.dumazet at gmail.com>:
> > On Wed, 2013-01-23 at 12:12 +0800, Frank Li wrote:
> >> Add napi support
> >>
> >> Before this patch
> >>
> >> iperf -s -i 1
> >> ------------------------------------------------------------
> >> Server listening on TCP port 5001
> >> TCP window size: 85.3 KByte (default)
> >> ------------------------------------------------------------
> >> [ 4] local 10.192.242.153 port 5001 connected with 10.192.242.138 port 50004
> >> [ ID] Interval Transfer Bandwidth
> >> [ 4] 0.0- 1.0 sec 41.2 MBytes 345 Mbits/sec
> >> [ 4] 1.0- 2.0 sec 43.7 MBytes 367 Mbits/sec
> >> [ 4] 2.0- 3.0 sec 42.8 MBytes 359 Mbits/sec
> >> [ 4] 3.0- 4.0 sec 43.7 MBytes 367 Mbits/sec
> >> [ 4] 4.0- 5.0 sec 42.7 MBytes 359 Mbits/sec
> >> [ 4] 5.0- 6.0 sec 43.8 MBytes 367 Mbits/sec
> >> [ 4] 6.0- 7.0 sec 43.0 MBytes 361 Mbits/sec
> >>
> >> After this patch
> >> [ 4] 2.0- 3.0 sec 51.6 MBytes 433 Mbits/sec
> >> [ 4] 3.0- 4.0 sec 51.8 MBytes 435 Mbits/sec
> >> [ 4] 4.0- 5.0 sec 52.2 MBytes 438 Mbits/sec
> >> [ 4] 5.0- 6.0 sec 52.1 MBytes 437 Mbits/sec
> >> [ 4] 6.0- 7.0 sec 52.1 MBytes 437 Mbits/sec
> >> [ 4] 7.0- 8.0 sec 52.3 MBytes 439 Mbits/sec
> >
> > Strange, as you still call netif_rx()
> >
> > NAPI should call netif_receive_skb() instead
> >
>
> Thank you point out.
> After re-test, I found performance is almost no change if use netif_receive_skb.
> I am not sure if it is my NAPI implement problem.
>
> napi_gro_received is better than netif_receive_skb, but worse than netif_rx.
>
> From performance point view,
>
> netif_rx --- fastest
> napi_gro_received --- middle, near to netif_rx
> netif_receive_skb --- slowest, almost the same as original no-napi version.
>
> Do you have any idea about this phenomena?
No idea, you'll have to find out using perf tool if available.
Is your machine SMP, and the application running on another cpu than the
softirq handler for your device ?
A NAPI driver must call netif_receive_skb(), especially if
the RX path does a full copy of the frame : Its hot in cpu cache and
should be processed at once.
Escaping to netif_rx() is only adding an extra softirq and risk of data
being evicted from cpu caches.
Here your performance increase only comes from hw_lock being not anymore
locked in RX path.
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