Hello Jamal,
On Wed, Mar 19, 2025 at 05:05:08PM -0400, Jamal Hadi Salim wrote:
> On Wed, Mar 19, 2025 at 2:12 PM Breno Leitao <lei...@debian.org> wrote:
> >
> > On Wed, Mar 19, 2025 at 09:05:07AM -0700, Paul E. McKenney wrote:
> >
> > > > I think we should redesign lockdep_unregister_key() to work on a
> > > > separately
> > > > allocated piece of memory,
> > > > then use kfree_rcu() in it.
> > > >
> > > > Ie not embed a "struct lock_class_key" in the struct Qdisc, but a
> > > > pointer to
> > > >
> > > > struct ... {
> > > > struct lock_class_key;
> > > > struct rcu_head rcu;
> > > > }
> > >
> > > Works for me!
> >
> > I've tested a different approach, using synchronize_rcu_expedited()
> > instead of synchronize_rcu(), given how critical this function is
> > called, and the command performance improves dramatically.
> >
> > This approach has some IPI penalties, but, it might be quicker to review
> > and get merged, mitigating the network issue.
> >
> > Does it sound a bad approach?
> >
> > Date: Wed Mar 19 10:23:56 2025 -0700
> >
> > lockdep: Speed up lockdep_unregister_key() with expedited RCU
> > synchronization
> >
> > lockdep_unregister_key() is called from critical code paths, including
> > sections where rtnl_lock() is held. When replacing a qdisc in a network
> > device, network egress traffic is disabled while __qdisc_destroy() is
> > called for every queue. This function calls lockdep_unregister_key(),
> > which was blocked waiting for synchronize_rcu() to complete.
> >
> > For example, a simple tc command to replace a qdisc could take 13
> > seconds:
> >
> > # time /usr/sbin/tc qdisc replace dev eth0 root handle 0x1234: mq
> > real 0m13.195s
> > user 0m0.001s
> > sys 0m2.746s
> >
>
> Could you please add the "after your change" output as well?
Sure. I will send the official patch tomorrow, and I will update it with
the information as well.
Thanks
--breno
