netdev - RE: [PATCH v1 6/6] net: fec: Add software TSO support

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Date:	Sun, 1 Jun 2014 02:25:46 +0000
From:	"fugang.duan@...escale.com" <fugang.duan@...escale.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	"Frank.Li@...escale.com" <Frank.Li@...escale.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"ezequiel.garcia@...e-electrons.com" 
	<ezequiel.garcia@...e-electrons.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"bhutchings@...arflare.com" <bhutchings@...arflare.com>,
	"stephen@...workplumber.org" <stephen@...workplumber.org>
Subject: RE: [PATCH v1 6/6] net: fec: Add software TSO support

From: Eric Dumazet <eric.dumazet@...il.com> Data: Sunday, June 01, 2014 9:40 AM
>To: Duan Fugang-B38611
>Cc: Li Frank-B20596; davem@...emloft.net; ezequiel.garcia@...e-
>electrons.com; netdev@...r.kernel.org; shawn.guo@...aro.org;
>bhutchings@...arflare.com; stephen@...workplumber.org
>Subject: RE: [PATCH v1 6/6] net: fec: Add software TSO support
>
>On Sun, 2014-06-01 at 00:55 +0000, fugang.duan@...escale.com wrote:
>> From: Eric Dumazet <eric.dumazet@...il.com> Data: Saturday, May 31,
>> 2014 12:22 AM
>> So I connect to APPLE MAC book to test again, test result (applied the
>patches to our internal kernel 3.10.31):
>> High mem disable: tx bandwidth 942Mbps, cpu loading is 65%.
>> High mem enable: tx bandwidth 930Mbps, cpu loading is 100%.
>> => I don't know why kernel highmem config enable cause so much
>performance drop ???
>>
>> For your above suggestion "using one descriptor per MSS, instead of two":
>> Yes, for imx6dl soc, we just do it like this.  For imx6sx soc FEC that
>support byte alignment,  so it also use one descriptor per MSS.
>>
>> Thanks for your suggestion and response. Do you know why highmem cause
>much performance drop for SW TSO ?
>
>Check NETIF_F_HIGHDMA : your driver might be able to advertise its support.
>
Indeed, I got the test result after add "NETIF_F_HIGHDMA" feature, otherwise, the performance is worse.

>Check your copies, because you might then need kmap()
>
>For an example, read efx_skb_copy_bits_to_pio() in
>drivers/net/ethernet/sfc/tx.c
>
I will check it.

Thanks,
Andy