netdev - Re: [PATCH net-next] doc: document MSG

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Message-ID: <20170901021007.pkbb2gsipbprf4w7@ast-mbp>
Date:   Thu, 31 Aug 2017 19:10:09 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] doc: document MSG_ZEROCOPY

On Thu, Aug 31, 2017 at 05:00:13PM -0400, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> Documentation for this feature was missing from the patchset.
> Copied a lot from the netdev 2.1 paper, addressing some small
> interface changes since then.
> 
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
...
> +Notification Batching
> +~~~~~~~~~~~~~~~~~~~~~
> +
> +Multiple outstanding packets can be read at once using the recvmmsg
> +call. This is often not needed. In each message the kernel returns not
> +a single value, but a range. It coalesces consecutive notifications
> +while one is outstanding for reception on the error queue.
> +
> +When a new notification is about to be queued, it checks whether the
> +new value extends the range of the notification at the tail of the
> +queue. If so, it drops the new notification packet and instead increases
> +the range upper value of the outstanding notification.

Would it make sense to mention that max notification range is 32-bit?
So each 4Gbyte of xmit bytes there will be a notification.
In modern 40Gbps NICs it's not a lot. Means that there will be
at least one notification every second.
Or I misread the code?

Thanks for the doc!

Acked-by: Alexei Starovoitov <ast@...nel.org>