On Wed, Jul 23, 2008 at 11:03:06AM +0200, Peter Zijlstra wrote:

On Wed, 2008-07-23 at 08:54 +0000, Jarek Poplawski wrote:

quoted

On Wed, Jul 23, 2008 at 12:59:21AM -0700, David Miller wrote:

quoted

From: Jarek Poplawski <redacted>
Date: Wed, 23 Jul 2008 06:20:36 +0000

quoted

PS: if there is nothing new in lockdep the classical method would
be to change this static array:

static struct lock_class_key
netdev_xmit_lock_key[ARRAY_SIZE(netdev_lock_type)];

to

static struct lock_class_key
netdev_xmit_lock_key[ARRAY_SIZE(netdev_lock_type)][MAX_NUM_TX_QUEUES];

and set lockdep classes per queue as well. (If we are sure we don't
need lockdep subclasses anywhere this could be optimized by using
one lock_class_key per 8 queues and spin_lock_nested()).

Unfortunately MAX_NUM_TX_QUEUES is USHORT_MAX, so this isn't really
a feasible approach.

Is it used by real devices already? Maybe for the beginning we could
start with something less?

quoted

spin_lock_nested() isn't all that viable either, as the subclass
limit is something like 8.

This method would need to do some additional counting: depending of
a queue number each 8 subsequent queues share (are set to) the same
class and their number mod 8 gives the subqueue number for
spin_lock_nested().

I'll try to find if there is something new around this in lockdep.
(lockdep people added to CC.)

There isn't.

Is there a static data structure that the driver needs to instantiate to
'create' a queue? Something like:

/* this imaginary e1000 hardware has 16 hardware queues */
static struct net_tx_queue e1000e_tx_queues[16]; 

I guess, not.

Then, IMHO, we could be practical and simply skip lockdep validation
for "some" range of locks: e.g. to set the table for the first 256
queues only, and to do e.g. __raw_spin_lock() for bigger numbers. (If
there are any bad locking patterns this should be enough for checking.)

Jarek P.
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