vlan patch

[Gleb Smirnoff]

On Fri, Oct 21, 2005 at 10:06:55AM +0400, Yar Tikhiy wrote:
Y> On Fri, Oct 21, 2005 at 09:30:33AM +0400, Gleb Smirnoff wrote:
Y> > On Thu, Oct 20, 2005 at 12:57:21PM +0400, Yar Tikhiy wrote:
Y> > Y> The hash code consists of literally a couple of #define's.  And the
Y> > Y> difference between ng_vlan(4) and vlan(4) is that each ng_vlan node
Y> > Y> gets its own instance of the hash table.  OTOH, in vlan(4) we need
Y> > Y> to decide if the hash table will be per parent interface or a single
Y> > Y> global instance.  In the latter case we could hash by a combination
Y> > Y> of the VLAN tag and parent's ifindex.  Perhaps this approach will
Y> > Y> yield more CPU cache hits during hash table lookups.  In addition,
Y> > Y> it will be thriftier in using memory.  Locking the global hash table
Y> > Y> should not be an issue as we can use an sx lock in this case for
Y> > Y> optimal read access.
Y> > 
Y> > The sx lock is slow. We'd better use per interface hash, and thus
Y> > get locking instantly, with per-vlan lock. In other case, we will
Y> > acquire per-vlan lock + the sx lock on every packet. The sx lock
Y> > actually means mtx_lock+mtx_unlock, thus we will make 3 mutex
Y> > operations instead of one.
Y> 
Y> OK, let's forget about sx locks.  However, a per-interface hash is
Y> associated with a _physical_ interface, hence we must find the vlan
Y> to lock using the hash first.  If there were a physical interface
Y> lock held by its driver in each case, it could protect the hash as
Y> well.  Can we rely on this?

Oops. When speaking about per-vlan lock, I really meant per-trunk lock. 

Or are you going to implement per-vlan lock? Is this going to be a benefit?
Since all packets on trunk are serialized by NIC driver, can there be any
benefit in creating a mutex per vlan interface, not per vlan trunk?

-- 
Totus tuus, Glebius.
GLEBIUS-RIPN GLEB-RIPE