netdev - Re: [PATCH net-next 1/3] ibmvnic: Enable scatter-gather support

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Message-Id: <e5015ac2-d0f7-ff95-eea5-1adbedb13dc9@linux.vnet.ibm.com>
Date:   Thu, 26 Oct 2017 12:51:52 -0500
From:   Thomas Falcon <tlfalcon@...ux.vnet.ibm.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 1/3] ibmvnic: Enable scatter-gather support

On 10/18/2017 06:04 AM, David Laight wrote:
> From: Thomas Falcon
>> Sent: 17 October 2017 18:37
>> This patch enables scatter gather support. Since there is no
>> HW/FW scatter-gather support at this time, the driver needs to
>> loop through each fragment and copy it to a contiguous, pre-mapped
>> buffer entry.
> ...
>>  	offset = index * adapter->req_mtu;
>>  	dst = tx_pool->long_term_buff.buff + offset;
> You should be able to treat the pre-allocated data area as a
> big ring buffer.
> So it can hold a lot of small frames or a few big ones.
> This slightly complicates the 'is there enough space for
> this packet' check since you need buffer space as well
> as a ring entry.
>
> You also really want to align each tx buffer on a 4n+2
> boundary so that most of the copy is aligned.

Thanks for your comments. I'll try to address that in a future patch.

>
>>  	memset(dst, 0, adapter->req_mtu);
> Seems unnecessary.

I removed that bit, and so far you seem to be right :) .

Thanks,
Tom
>
> 	David
>