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

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6DD009AA16@AcuExch.aculab.com>
Date:   Wed, 18 Oct 2017 11:04:59 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Thomas Falcon' <tlfalcon@...ux.vnet.ibm.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next 1/3] ibmvnic: Enable scatter-gather support

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.

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

	David