netdev - Re: [PATCH] net: allow netdev_wait

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Date:	Fri, 30 Oct 2009 19:53:14 -0400
From:	Benjamin LaHaise <bcrl@...et.ca>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Octavian Purdila <opurdila@...acom.com>,
	netdev@...r.kernel.org, Cosmin Ratiu <cratiu@...acom.com>
Subject: Re: [PATCH] net: allow netdev_wait_allrefs() to run faster

On Fri, Oct 30, 2009 at 04:25:52PM -0700, Eric W. Biederman wrote:
> I realized after sending the message that s_mode in sysfs_dirent is a
> real size offense.  It is a 16bit field packed in between two longs.
> So in practice it is possible to move the s_mode  up next to s_flags
> and add a s_nlink after it both unsigned short and get a cheap sysfs_nlink.

That doesn't work -- the number of directory entries can easily exceed 65535.  
Current mid range hardware is good enough to terminate 100,000 network 
interfaces on a single host.

> Since I'm not quite ready to post my patches.  I will briefly
> mention what I have in my queue and hopefully get things posted.
> 
> I have changes to make it so that sysfs never has to go from
> the sysfs_dirent to the sysfs inode.  

Ah, interesting.

> I have changes to sys_sysctl() so that it becomes a filesystem lookup
> under /proc/sys.  Which ultimately makes the code easier to maintain
> and debug.

That sounds like a much saner approach, but has the wrinkle that procfs can 
be configured out.

> Now back to getting things forward ported and ready to post.

I'm looking forward to those changes.  I've been ignoring procfs for the 
time being by disabling the per-interface entries in the network stack, 
but there is some desire to be able to enable rp_filter on a per-interface 
radius config at runtime.  rp_filter has to be disabled across the board 
on my access routers, as there are several places where assymetric routing 
is used for performance reasons.

		-ben
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