netdev - Re: [PATCH RFC net-next 1/6] sock: MSG_PEEK support for sk_error

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Date:   Thu, 18 Jan 2018 18:03:41 -0500
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>, rds-devel@....oracle.com,
        santosh.shilimkar@...cle.com
Subject: Re: [PATCH RFC net-next 1/6] sock: MSG_PEEK support for
 sk_error_queue

On (01/18/18 17:54), Willem de Bruijn wrote:
> > 2. If we have the option of passing completion-notification up as ancillary
> >    data on the pollin/recvmsg channel itself (instead of MSG_ERRQUEUE)
> 
> This assumes a somewhat symmetric workload, where there are enough recv
> calls to reap the notification associated with the send calls.

Your comment about the assumption is true, but at least for the database
use-cases, we have a request-response model, so the assumption works out..
I dont know if many other workloads that send large buffers have this
pattern.

> I would stay with MSG_ERRQUEUE processing. One option is to pass data
> up to userspace in the data portion of the notification skb instead of
> encoding it in ancillary data, like tcp_get_timestamping_opt_stats.

that's similar to what I have, except that it does not have the
MSG_PEEK part (you'd need to enforce that the data portion
is upper-bounded, and that the application has the responsibility
of sending down "enough" buffer with recvmsg). 

Note that any one of these choices are ok with me- I have no
special attachments to any of them.

--Sowmini