netdev - Re: [net-next PATCH v1] net: netprio_cgroup: rework update socket logic

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Message-ID: <20120721020015.GA3827@neilslaptop.think-freely.org>
Date:	Fri, 20 Jul 2012 22:00:15 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	John Fastabend <john.r.fastabend@...el.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	eric.dumazet@...il.com, gaofeng@...fujitsu.com, lizefan@...wei.com
Subject: Re: [net-next PATCH v1] net: netprio_cgroup: rework update socket
 logic

On Fri, Jul 20, 2012 at 01:39:25PM -0700, John Fastabend wrote:
> Instead of updating the sk_cgrp_prioidx struct field on every send
> this only updates the field when a task is moved via cgroup
> infrastructure.
> 
> This allows sockets that may be used by a kernel worker thread
> to be managed. For example in the iscsi case today a user can
> put iscsid in a netprio cgroup and control traffic will be sent
> with the correct sk_cgrp_prioidx value set but as soon as data
> is sent the kernel worker thread isssues a send and sk_cgrp_prioidx
> is updated with the kernel worker threads value which is the
> default case.
> 
> It seems more correct to only update the field when the user
> explicitly sets it via control group infrastructure. This allows
> the users to manage sockets that may be used with other threads.
> 
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
I like the idea, but IIRC last time we tried this I think it caused problems
with processes that shared sockets.  That is to say, if you have a parent and
child process that dup an socket descriptior, and put them in separate cgroups,
you get unpredictable results, as the socket gets assigned a priority based on
the last processed that moved cgroups.

Neil

> 
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