netdev - Re: behavior of recvmmsg() on blocking sockets

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Date:	Wed, 24 Mar 2010 14:55:28 -0500
From:	Brandon Black <blblack@...il.com>
To:	Chris Friesen <cfriesen@...tel.com>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: behavior of recvmmsg() on blocking sockets

On Wed, Mar 24, 2010 at 2:36 PM, Chris Friesen <cfriesen@...tel.com> wrote:
> Note that I said "large numbers of sockets".  Like tens of thousands.
> In addition to context switch overhead this can also lead to issues with
> memory consumption due to stack frames.

Ok, agreed there.  In my case though, there will only ever be a
handful of sockets.  Ideally it would be just one socket.  The only
reason I allocate multiple sockets and spawn threads for them is
because you can't scale past one CPU core on a single socket, due to
the NIC and/or the driver and/or the socket locks and/or the basic
nature of the problem.

> Consider the case where you want to do some other useful work in
> addition to running your network server.  Every cpu cycle spent on the
> network server is robbed from the other work.  In this scenario you want
> to handle packets as efficiently as possible, so the timeout-based
> behaviour is better since it is more likely to give you multiple packets
> per syscall.

That's a good point, I tend to tunnelvision on the dedicated server
scenario.  I should probably have a user-level option for
timeout-based operation as well, since the decision here gets to the
systems admin/engineering level and will be situational.

Thanks,
-- Brandon
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