linux-kernel - Re: [PATCH 0/2] net: fs_enet: Remove non NAPI RX and add NAPI for TX

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Date:	Thu, 09 Oct 2014 07:23:53 +0200
From:	leroy christophe <christophe.leroy@....fr>
To:	David Miller <davem@...emloft.net>
CC:	pantelis.antoniou@...il.com, vbordug@...mvista.com,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH 0/2] net: fs_enet: Remove non NAPI RX and add NAPI for
 TX


Le 08/10/2014 22:03, David Miller a écrit :
> From: Christophe Leroy <christophe.leroy@....fr>
> Date: Tue,  7 Oct 2014 15:04:53 +0200 (CEST)
>
>> When using a MPC8xx as a router, 'perf' shows a significant time spent in
>> fs_enet_interrupt() and fs_enet_start_xmit().
>> 'perf annotate' shows that the time spent in fs_enet_start_xmit is indeed spent
>> between spin_unlock_irqrestore() and the following instruction, hence in
>> interrupt handling. This is due to the TX complete interrupt that fires after
>> each transmitted packet.
>> This patchset first remove all non NAPI handling as NAPI has become the only
>> mode for RX, then adds NAPI for handling TX complete.
>> This improves NAT TCP throughput by 21% on MPC885 with FEC.
>>
>> Tested on MPC885 with FEC.
>>
>> [PATCH 1/2] net: fs_enet: Remove non NAPI RX
>> [PATCH 2/2] net: fs_enet: Add NAPI TX
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> Series applied, thanks.
>
> Any particular reason you didn't just put the TX reclaim calls into
> the existing NAPI handler?
Not really. I used the gianfar.c driver as a model.
>
> That's what other drivers do, because TX reclaim can make SKBs
> available for RX packet receive on the local cpu.  So generally you
> have one NAPI context that first does any pending TX reclaim, then
> polls the RX ring for new packets.
>
Is that a better approach ?

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