On 4/14/2019 2:34 PM, Arend Van Spriel wrote:
On April 14, 2019 1:19:49 PM Felix Fietkau <nbd@xxxxxxxx> wrote:
On 2019-04-14 11:44, Arend Van Spriel wrote:
+ Herbert
On 3/16/2019 7:14 PM, Toke Høiland-Jørgensen wrote:
Felix Fietkau <nbd@xxxxxxxx> writes:
When using iTXQ, tx sequence number allocation and statistics are
run at
dequeue time. Because of that, it is safe to enable NETIF_F_LLTX,
which
allows tx handlers to run on multiple CPUs in parallel.
Cool, didn't know about that flag.
It is water under the bridge as this patch got applied already, but I
stumbled upon it just recently and didn't know about that flag either.
So I looked for more information about it and found the definition [1],
but the comment seemed important enough to send this reply.
NETIF_F_LLTX_BIT, /* LockLess TX - deprecated. Please */
/* do not use LLTX in new drivers */
Here is the commit that marked it deprecated:
commit e24eb521fbf2a350ce879dfc1d8e56d4ffa2aa22
Author: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Date: Tue Sep 25 19:42:02 2007 -0700
[NET]: note that NETIF_F_LLTX is deprecated
So I am not sure we should really do this in mac80211. Maybe Herbert can
comment although it has been over a decade ago.
There is a lot of comparable code that also uses this flag, e.g.
batman-adv, bridge, vlan, various tunnel implementations. I think
mac80211 fits well with those kinds of use cases.
Ok. As said I was not sure so I can/will not argue.
If I remember correctly, the deprecation was added to avoid quirky
custom locking schemes in ethernet drivers.
What do you mean by "quirky custom locking schemes"? You mean that TX
path would use driver data that should actually be accessed under some
lock?
When seeing the deprecated comment I wanted to know the why and was
hoping the commit message would divulge. It just mentions it is not
needed. So now I am curious as to why it wouldn't be needed especially
as you say there are (valid) use-cases in the kernel today.
Getting back to this in an attempt to clarify my question. So from what
Felix is saying the NETIF_F_LLTX flag is not deprecated, but restricted.
What I would like to know is what exactly is required from a driver to
allow the use of this flag.
Regards,
Arend
