Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 08:00:09PM +0200, Peter Zijlstra wrote: > On Tue, Jun 06, 2017 at 10:50:48AM -0700, Paul E. McKenney wrote: > > On Tue, Jun 06, 2017 at 07:23:42PM +0200, Peter Zijlstra wrote: > > > On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > > > > diff --git

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 08:00:09PM +0200, Peter Zijlstra wrote: > On Tue, Jun 06, 2017 at 10:50:48AM -0700, Paul E. McKenney wrote: > > On Tue, Jun 06, 2017 at 07:23:42PM +0200, Peter Zijlstra wrote: > > > On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > > > > diff --git

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 10:50:48AM -0700, Paul E. McKenney wrote: > On Tue, Jun 06, 2017 at 07:23:42PM +0200, Peter Zijlstra wrote: > > On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > > > index

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 10:50:48AM -0700, Paul E. McKenney wrote: > On Tue, Jun 06, 2017 at 07:23:42PM +0200, Peter Zijlstra wrote: > > On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > > > index

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 07:23:42PM +0200, Peter Zijlstra wrote: > On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > > index 3ae8474557df..157654fa436a 100644 > > --- a/kernel/rcu/srcutree.c > > +++

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 07:23:42PM +0200, Peter Zijlstra wrote: > On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > > index 3ae8474557df..157654fa436a 100644 > > --- a/kernel/rcu/srcutree.c > > +++

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > index 3ae8474557df..157654fa436a 100644 > --- a/kernel/rcu/srcutree.c > +++ b/kernel/rcu/srcutree.c > @@ -357,7 +357,7 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct); > >

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > index 3ae8474557df..157654fa436a 100644 > --- a/kernel/rcu/srcutree.c > +++ b/kernel/rcu/srcutree.c > @@ -357,7 +357,7 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct); > >

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 06:15:51PM +0200, Peter Zijlstra wrote: > On Tue, Jun 06, 2017 at 05:27:06PM +0200, Heiko Carstens wrote: > > On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: > > > > As a side note, I am asking myself, though, why we do need the > > >

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 06:15:51PM +0200, Peter Zijlstra wrote: > On Tue, Jun 06, 2017 at 05:27:06PM +0200, Heiko Carstens wrote: > > On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: > > > > As a side note, I am asking myself, though, why we do need the > > >

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 06:15:51PM +0200, Peter Zijlstra wrote: > On Tue, Jun 06, 2017 at 05:27:06PM +0200, Heiko Carstens wrote: > > On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: > > > > As a side note, I am asking myself, though, why we do need the > > >

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 06:15:51PM +0200, Peter Zijlstra wrote: > On Tue, Jun 06, 2017 at 05:27:06PM +0200, Heiko Carstens wrote: > > On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: > > > > As a side note, I am asking myself, though, why we do need the > > >

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 05:27:06PM +0200, Heiko Carstens wrote: > On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: > > As a side note, I am asking myself, though, why we do need the > > preempt_disable/enable for the cases where we use the opcodes > > like lao (atomic load

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 05:27:06PM +0200, Heiko Carstens wrote: > On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: > > As a side note, I am asking myself, though, why we do need the > > preempt_disable/enable for the cases where we use the opcodes > > like lao (atomic load

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: > A the same time, the implicit memory barrier of the atomic_inc should be > even cheaper. In contrast to x86, a full smp_mb seems to be almost for > free (looks like <= 1 cycle for a bcr 14,0 and no contention). So I > _think_

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: > A the same time, the implicit memory barrier of the atomic_inc should be > even cheaper. In contrast to x86, a full smp_mb seems to be almost for > free (looks like <= 1 cycle for a bcr 14,0 and no contention). So I > _think_

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 03:08:50PM +0200, Paolo Bonzini wrote: > > > On 06/06/2017 12:53, Peter Zijlstra wrote: > > On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > >> There would be a slowdown if 1) fast this_cpu_inc is not available and > >> cannot be implemented (this

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 03:08:50PM +0200, Paolo Bonzini wrote: > > > On 06/06/2017 12:53, Peter Zijlstra wrote: > > On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > >> There would be a slowdown if 1) fast this_cpu_inc is not available and > >> cannot be implemented (this

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 05:54:28PM +0200, Peter Zijlstra wrote: > On Tue, Jun 06, 2017 at 05:53:57AM -0700, Paul E. McKenney wrote: > > So the only part of this patch that is needed is the changes to the > > comments, right? ;-) > > Right, although I would suggest putting that requirement (the

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 05:54:28PM +0200, Peter Zijlstra wrote: > On Tue, Jun 06, 2017 at 05:53:57AM -0700, Paul E. McKenney wrote: > > So the only part of this patch that is needed is the changes to the > > comments, right? ;-) > > Right, although I would suggest putting that requirement (the

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 05:37:05PM +0200, Christian Borntraeger wrote: > On 06/06/2017 05:27 PM, Heiko Carstens wrote: > > On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: > >> Adding s390 folks and list > Only s390 is TSO, arm64 is very much a weak arch. > >>> > >>>

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 05:37:05PM +0200, Christian Borntraeger wrote: > On 06/06/2017 05:27 PM, Heiko Carstens wrote: > > On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: > >> Adding s390 folks and list > Only s390 is TSO, arm64 is very much a weak arch. > >>> > >>>

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 05:53:57AM -0700, Paul E. McKenney wrote: > So the only part of this patch that is needed is the changes to the > comments, right? ;-) Right, although I would suggest putting that requirement (the balanced lock vs unlock) somewhere as well.

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 05:53:57AM -0700, Paul E. McKenney wrote: > So the only part of this patch that is needed is the changes to the > comments, right? ;-) Right, although I would suggest putting that requirement (the balanced lock vs unlock) somewhere as well.

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On 06/06/2017 05:27 PM, Heiko Carstens wrote: > On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: >> Adding s390 folks and list Only s390 is TSO, arm64 is very much a weak arch. >>> >>> Right, and thus arm64 can implement a fast this_cpu_inc using LL/SC. >>> s390 cannot

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On 06/06/2017 05:27 PM, Heiko Carstens wrote: > On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: >> Adding s390 folks and list Only s390 is TSO, arm64 is very much a weak arch. >>> >>> Right, and thus arm64 can implement a fast this_cpu_inc using LL/SC. >>> s390 cannot

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: > Adding s390 folks and list > >> Only s390 is TSO, arm64 is very much a weak arch. > > > > Right, and thus arm64 can implement a fast this_cpu_inc using LL/SC. > > s390 cannot because its atomic_inc has implicit memory

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 04:45:57PM +0200, Christian Borntraeger wrote: > Adding s390 folks and list > >> Only s390 is TSO, arm64 is very much a weak arch. > > > > Right, and thus arm64 can implement a fast this_cpu_inc using LL/SC. > > s390 cannot because its atomic_inc has implicit memory

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

Adding s390 folks and list On 06/06/2017 03:08 PM, Paolo Bonzini wrote: > > > On 06/06/2017 12:53, Peter Zijlstra wrote: >> On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: >>> There would be a slowdown if 1) fast this_cpu_inc is not available and >>> cannot be implemented

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

Adding s390 folks and list On 06/06/2017 03:08 PM, Paolo Bonzini wrote: > > > On 06/06/2017 12:53, Peter Zijlstra wrote: >> On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: >>> There would be a slowdown if 1) fast this_cpu_inc is not available and >>> cannot be implemented

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On 06/06/2017 12:53, Peter Zijlstra wrote: > On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: >> There would be a slowdown if 1) fast this_cpu_inc is not available and >> cannot be implemented (this usually means that atomic_inc has implicit >> memory barriers), > > I don't get

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On 06/06/2017 12:53, Peter Zijlstra wrote: > On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: >> There would be a slowdown if 1) fast this_cpu_inc is not available and >> cannot be implemented (this usually means that atomic_inc has implicit >> memory barriers), > > I don't get

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 12:53:43PM +0200, Peter Zijlstra wrote: > On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > > There would be a slowdown if 1) fast this_cpu_inc is not available and > > cannot be implemented (this usually means that atomic_inc has implicit > > memory

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 12:53:43PM +0200, Peter Zijlstra wrote: > On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > > There would be a slowdown if 1) fast this_cpu_inc is not available and > > cannot be implemented (this usually means that atomic_inc has implicit > > memory

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 02:01:54PM +0200, Paolo Bonzini wrote: > > > On 06/06/2017 13:09, Peter Zijlstra wrote: > >> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c > >> index 36e1f82faed1..681bf6bc04a5 100644 > >> --- a/kernel/rcu/srcutiny.c > >> +++ b/kernel/rcu/srcutiny.c > >> @@

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Tue, Jun 06, 2017 at 02:01:54PM +0200, Paolo Bonzini wrote: > > > On 06/06/2017 13:09, Peter Zijlstra wrote: > >> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c > >> index 36e1f82faed1..681bf6bc04a5 100644 > >> --- a/kernel/rcu/srcutiny.c > >> +++ b/kernel/rcu/srcutiny.c > >> @@

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On 06/06/2017 13:09, Peter Zijlstra wrote: >> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c >> index 36e1f82faed1..681bf6bc04a5 100644 >> --- a/kernel/rcu/srcutiny.c >> +++ b/kernel/rcu/srcutiny.c >> @@ -35,8 +35,8 @@ >> >> static int init_srcu_struct_fields(struct srcu_struct

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On 06/06/2017 13:09, Peter Zijlstra wrote: >> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c >> index 36e1f82faed1..681bf6bc04a5 100644 >> --- a/kernel/rcu/srcutiny.c >> +++ b/kernel/rcu/srcutiny.c >> @@ -35,8 +35,8 @@ >> >> static int init_srcu_struct_fields(struct srcu_struct

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c > index 36e1f82faed1..681bf6bc04a5 100644 > --- a/kernel/rcu/srcutiny.c > +++ b/kernel/rcu/srcutiny.c > @@ -35,8 +35,8 @@ > > static int init_srcu_struct_fields(struct srcu_struct *sp) > { > - sp->srcu_lock_nesting[0] = 0; > -

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c > index 36e1f82faed1..681bf6bc04a5 100644 > --- a/kernel/rcu/srcutiny.c > +++ b/kernel/rcu/srcutiny.c > @@ -35,8 +35,8 @@ > > static int init_srcu_struct_fields(struct srcu_struct *sp) > { > - sp->srcu_lock_nesting[0] = 0; > -

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > There would be a slowdown if 1) fast this_cpu_inc is not available and > cannot be implemented (this usually means that atomic_inc has implicit > memory barriers), I don't get this. How is per-cpu crud related to being strongly

Re: [PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

On Mon, Jun 05, 2017 at 03:09:50PM -0700, Paul E. McKenney wrote: > There would be a slowdown if 1) fast this_cpu_inc is not available and > cannot be implemented (this usually means that atomic_inc has implicit > memory barriers), I don't get this. How is per-cpu crud related to being strongly

[PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

From: Paolo Bonzini Linu Cherian reported a WARN in cleanup_srcu_struct when shutting down a guest that has iperf running on a VFIO assigned device. This happens because irqfd_wakeup calls srcu_read_lock(>irq_srcu) in interrupt context, while a worker thread does the same

[PATCH RFC tip/core/rcu 1/2] srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context

From: Paolo Bonzini Linu Cherian reported a WARN in cleanup_srcu_struct when shutting down a guest that has iperf running on a VFIO assigned device. This happens because irqfd_wakeup calls srcu_read_lock(>irq_srcu) in interrupt context, while a worker thread does the same inside kvm_set_irq.