netdev - Re: [RFC][PATCH 2/2] bgmac: pass received packet to the netif instead of copying it

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Message-ID: <CACna6rwtLw-Aiz3amMvTBwWsi0OWo5f2yMCF9e8DeCjKLOGDEA@mail.gmail.com>
Date:	Thu, 15 Aug 2013 13:36:48 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	Network Development <netdev@...r.kernel.org>,
	OpenWrt Development List <openwrt-devel@...ts.openwrt.org>,
	Hauke Mehrtens <hauke@...ke-m.de>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jonas Gorski <jogo@...nwrt.org>,
	Robert Bradley <robert.bradley1@...il.com>
Subject: Re: [RFC][PATCH 2/2] bgmac: pass received packet to the netif instead
 of copying it

2013/8/11 Rafał Miłecki <zajec5@...il.com>:
> It makes more sense to allocate new (empty) skb and pass it to the
> hardware. That way we avoid copying whole packet into new skb which
> should result in better performance.

I did some testing of this patch using "perf" tool and iperf -s
running on the OpenWrt machine (with bgmac supported hardware).

There are the results:
No network usage:
64.93% [kernel] [k] arch_cpu_idle
16.10% [kernel] [k] arch_local_irq_restore
11.52% [kernel] [k] cpu_startup_entry

Running iperf on PC: iperf -c 192.168.1.1
23.57% [kernel] [k] __copy_user_common
10.57% [kernel] [k] csum_partial
8.87% [kernel] [k] arch_cpu_idle
4.74% [kernel] [k] arch_local_irq_restore
4.30% [ip_tables] [k] ipt_do_table
2.91% [nf_conntrack] [k] nf_conntrack_in
2.44% [kernel] [k] __netif_receive_skb_core
2.36% [kernel] [k] r4k_dma_cache_inv
2.33% [nf_conntrack] [k] nf_conntrack_proto_fini

With 0002-bgmac-pass-received-packet-to-the-netif-instead-of-c.patch
14.83% [kernel] [k] __copy_user_common
14.81% [kernel] [k] csum_partial
4.24% [ip_tables] [k] ipt_do_table
3.69% [kernel] [k] arch_local_irq_restore
3.54% [kernel] [k] __netif_receive_skb_core
3.38% [kernel] [k] r4k_dma_cache_inv
3.24% [nf_conntrack] [k] nf_conntrack_in
2.95% [xt_conntrack] [k] 0x0000018c
2.88% [nf_conntrack] [k] nf_conntrack_proto_fini
2.58% [iptable_nat] [k] 0x00000008
2.32% [bgmac] [k] 0x00000d9c
2.18% [nf_conntrack_ipv4] [k] need_ipv4_conntrack

So you can see that __copy_user_common usage has really decreased with
this patch!

Unfortunately it didn't result in better performance... no idea why :(

-- 
Rafał
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