netdev - Re: [PATCH net-next v2] unix: add read side socket memory accounting for dgram sockets

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Date:	Tue, 4 Mar 2014 21:13:36 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, yannick@...hler.name,
	eric.dumazet@...il.com, xiyou.wangcong@...il.com, dan@...dstab.net
Subject: Re: [PATCH net-next v2] unix: add read side socket memory accounting for dgram sockets

On Wed, Feb 26, 2014 at 03:42:32PM -0500, David Miller wrote:
> From: Hannes Frederic Sowa <hannes@...essinduktion.org>
> Date: Wed, 26 Feb 2014 21:21:54 +0100
> 
> > On Wed, Feb 26, 2014 at 02:55:59PM -0500, David Miller wrote:
> >> I think you can safely put the 'other' sock pointer into the control
> >> block.  Because when we disassociate from a peer any pending packets
> >> in flight to him will be consumed/dropped, so there can't be any
> >> lingering references, right?
> > 
> > I am afraid lingering socket references will happen if the sockets are
> > used in unconnected mode.
> 
> Sigh...
> 
> Ok, let's wait for your hackbench results and work from there.

Just a small followup:

Because of the additional sock_wfree during skb handover in unix_dgram_sendmsg
the spinlock in __wake_up_sync_key is hit more often thus more cacheline
bouncing.

Deferring the POLLOUT notification after the sock_rfree in unix_dgram_recvmsg
already halfed the number of context switches with the new patch.

I try to play with some other ideas this week and will submit new patch with
performance numbers.

Haven't noticed any problems with the additional atomic operations
performance-wise so far.

Bye,

  Hannes

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