netdev - Re: [RFC/PATCH] sungem: Spring cleaning and GRO support

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Date:	Wed, 01 Jun 2011 01:04:59 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	"R. Herbst" <ruediger.herbst@...glemail.com>,
	Brian Hamilton <bhamilton04@...il.com>
Subject: Re: [RFC/PATCH] sungem: Spring cleaning and GRO support

On Wed, 2011-06-01 at 09:55 +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2011-05-31 at 23:17 +0100, Ben Hutchings wrote:
> > On Wed, 2011-06-01 at 07:58 +1000, Benjamin Herrenschmidt wrote:
> > [...]
> > > > Is the pm_mutex really needed?  All control operations should already be
> > > > serialised by the RTNL lock, and you've started taking that in the
> > > > suspend and resume functions.
> > > 
> > > Well, it's been there forever and I need to get my head around it, but
> > > yes, the rtnl lock might be able to get rid of it, good point. I just
> > > actually added that :-)
> > > 
> > > So all ndo_set_* are going to be covered by rtnl including the ethtool ?
> > 
> > ethtool ops are almost all covered; the kernel-doc comment has the
> > details.
> > 
> > As for net_device_ops, locking varies (and really ought to be documented
> > in <linux/netdevice.h>).  At least ndo_set_mac_address, ndo_change_mtu
> > and ndo_do_ioctl (plus of course ndo_open and ndo_stop) are called
> > holding the RTNL lock.
> 
> Ok. The main annoyance for locking has always been set_multicast which
> is called with a spinlock afaik.

Right, that's called with the address-list spinlock (and previously with
the TX spinlock, I think).  In sfc we defer multicast reconfiguration to
a work item since it can require process context.

> > > I don't really want to take the rtnl lock in the reset task (at least
> > > not for the whole duration of it), so I may have to be a bit creative on
> > > synchronization there.
> > [...]
> > 
> > Unless reset takes more than a second I wouldn't worry about it.
> 
> I don't want to take a spinlock for even near that, especially since we
> do the reset on every link down. I suppose rtnl might be less of an
> issue, I'll have a look.

So long as you aren't holding it for, say, blinking an LED indefinitely
it's fine... :-)

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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