* [PATCH 0/3] some improvements for lockdep
@ 2021-06-17 14:28 Xiongwei Song
2021-06-17 14:28 ` [PATCH 1/3] locking/lockdep: unlikely bfs_error() inside Xiongwei Song
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Xiongwei Song @ 2021-06-17 14:28 UTC (permalink / raw)
To: peterz, mingo, will, longman, boqun.feng; +Cc: linux-kernel, Xiongwei Song
Unlikely the checks of return values of graph walk will improve the
performance to some degree, patch 1 and patch 2 are for this.
The patch 3 will print a warning after counting lock deps when hitting
bfs errors.
Xiongwei Song (3):
locking/lockdep: unlikely bfs_error function
locking/lockdep: unlikely conditons about BFS_RMATCH
locking/lockdep: print possible warning after counting deps
kernel/locking/lockdep.c | 22 +++++++++++++++-------
1 file changed, 15 insertions(+), 7 deletions(-)
--
2.30.2
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH 1/3] locking/lockdep: unlikely bfs_error() inside
2021-06-17 14:28 [PATCH 0/3] some improvements for lockdep Xiongwei Song
@ 2021-06-17 14:28 ` Xiongwei Song
2021-06-17 14:28 ` [PATCH 2/3] locking/lockdep: unlikely conditons about BFS_RMATCH Xiongwei Song
2021-06-17 14:28 ` [PATCH 3/3] locking/lockdep: print possible warning after counting deps Xiongwei Song
2 siblings, 0 replies; 6+ messages in thread
From: Xiongwei Song @ 2021-06-17 14:28 UTC (permalink / raw)
To: peterz, mingo, will, longman, boqun.feng; +Cc: linux-kernel, Xiongwei Song
From: Xiongwei Song <sxwjean@gmail.com>
The error from graph walk is small probability event, and there are some
bfs_error calls during lockdep detection, so unlikely bfs_error inside
can improve performance a little bit.
Suggested-by: Waiman Long <longman@redhat.com>
Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
---
kernel/locking/lockdep.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 7641bd407239..a8a66a2a9bc1 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1540,7 +1540,7 @@ enum bfs_result {
*/
static inline bool bfs_error(enum bfs_result res)
{
- return res < 0;
+ return unlikely(res < 0);
}
/*
@@ -2089,7 +2089,7 @@ check_path(struct held_lock *target, struct lock_list *src_entry,
ret = __bfs_forwards(src_entry, target, match, skip, target_entry);
- if (unlikely(bfs_error(ret)))
+ if (bfs_error(ret))
print_bfs_bug(ret);
return ret;
@@ -2936,7 +2936,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
* in the graph whose neighbours are to be checked.
*/
ret = check_noncircular(next, prev, trace);
- if (unlikely(bfs_error(ret) || ret == BFS_RMATCH))
+ if (bfs_error(ret) || unlikely(ret == BFS_RMATCH))
return 0;
if (!check_irq_usage(curr, prev, next))
--
2.30.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH 2/3] locking/lockdep: unlikely conditons about BFS_RMATCH
2021-06-17 14:28 [PATCH 0/3] some improvements for lockdep Xiongwei Song
2021-06-17 14:28 ` [PATCH 1/3] locking/lockdep: unlikely bfs_error() inside Xiongwei Song
@ 2021-06-17 14:28 ` Xiongwei Song
2021-06-17 14:28 ` [PATCH 3/3] locking/lockdep: print possible warning after counting deps Xiongwei Song
2 siblings, 0 replies; 6+ messages in thread
From: Xiongwei Song @ 2021-06-17 14:28 UTC (permalink / raw)
To: peterz, mingo, will, longman, boqun.feng; +Cc: linux-kernel, Xiongwei Song
From: Xiongwei Song <sxwjean@gmail.com>
The probability that graph walk will return BFS_RMATCH is slim, so unlikey
conditons about BFS_RMATCH can improve performance a little bit.
Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
---
kernel/locking/lockdep.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index a8a66a2a9bc1..cb94097014d8 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2750,7 +2750,7 @@ check_redundant(struct held_lock *src, struct held_lock *target)
*/
ret = check_path(target, &src_entry, hlock_equal, usage_skip, &target_entry);
- if (ret == BFS_RMATCH)
+ if (unlikely(ret == BFS_RMATCH))
debug_atomic_inc(nr_redundant);
return ret;
@@ -2992,7 +2992,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
ret = check_redundant(prev, next);
if (bfs_error(ret))
return 0;
- else if (ret == BFS_RMATCH)
+ else if (unlikely(ret == BFS_RMATCH))
return 2;
if (!*trace) {
--
2.30.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH 3/3] locking/lockdep: print possible warning after counting deps
2021-06-17 14:28 [PATCH 0/3] some improvements for lockdep Xiongwei Song
2021-06-17 14:28 ` [PATCH 1/3] locking/lockdep: unlikely bfs_error() inside Xiongwei Song
2021-06-17 14:28 ` [PATCH 2/3] locking/lockdep: unlikely conditons about BFS_RMATCH Xiongwei Song
@ 2021-06-17 14:28 ` Xiongwei Song
2021-06-17 15:12 ` Boqun Feng
2 siblings, 1 reply; 6+ messages in thread
From: Xiongwei Song @ 2021-06-17 14:28 UTC (permalink / raw)
To: peterz, mingo, will, longman, boqun.feng; +Cc: linux-kernel, Xiongwei Song
From: Xiongwei Song <sxwjean@gmail.com>
The graph walk might hit error when counting dependencies. Once the
return value is negative, print a warning to reminder users.
Suggested-by: Waiman Long <longman@redhat.com>
Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
---
kernel/locking/lockdep.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index cb94097014d8..cfe0f4374594 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2028,8 +2028,12 @@ static unsigned long __lockdep_count_forward_deps(struct lock_list *this)
{
unsigned long count = 0;
struct lock_list *target_entry;
+ enum bfs_result ret;
+
+ ret = __bfs_forwards(this, (void *)&count, noop_count, NULL, &target_entry);
- __bfs_forwards(this, (void *)&count, noop_count, NULL, &target_entry);
+ if (bfs_error(ret))
+ print_bfs_bug(ret);
return count;
}
@@ -2053,8 +2057,12 @@ static unsigned long __lockdep_count_backward_deps(struct lock_list *this)
{
unsigned long count = 0;
struct lock_list *target_entry;
+ enum bfs_result ret;
+
+ ret = __bfs_backwards(this, (void *)&count, noop_count, NULL, &target_entry);
- __bfs_backwards(this, (void *)&count, noop_count, NULL, &target_entry);
+ if (bfs_error(ret))
+ print_bfs_bug(ret);
return count;
}
--
2.30.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH 3/3] locking/lockdep: print possible warning after counting deps
2021-06-17 14:28 ` [PATCH 3/3] locking/lockdep: print possible warning after counting deps Xiongwei Song
@ 2021-06-17 15:12 ` Boqun Feng
2021-06-18 1:54 ` Xiongwei Song
0 siblings, 1 reply; 6+ messages in thread
From: Boqun Feng @ 2021-06-17 15:12 UTC (permalink / raw)
To: Xiongwei Song; +Cc: peterz, mingo, will, longman, linux-kernel, Xiongwei Song
Hi,
On Thu, Jun 17, 2021 at 10:28:28PM +0800, Xiongwei Song wrote:
> From: Xiongwei Song <sxwjean@gmail.com>
>
> The graph walk might hit error when counting dependencies. Once the
> return value is negative, print a warning to reminder users.
>
Thanks for the improvement, but please see below:
> Suggested-by: Waiman Long <longman@redhat.com>
> Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
> ---
> kernel/locking/lockdep.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index cb94097014d8..cfe0f4374594 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -2028,8 +2028,12 @@ static unsigned long __lockdep_count_forward_deps(struct lock_list *this)
> {
> unsigned long count = 0;
> struct lock_list *target_entry;
> + enum bfs_result ret;
> +
> + ret = __bfs_forwards(this, (void *)&count, noop_count, NULL, &target_entry);
>
> - __bfs_forwards(this, (void *)&count, noop_count, NULL, &target_entry);
> + if (bfs_error(ret))
> + print_bfs_bug(ret);
Here print_bfs_bug() will eventually call debug_locks_off_graph_unlock()
to release the graph lock, and the caller (lockdep_count_fowards_deps())
will also call graph_unlock() afterwards, and that means we unlock
*twice* if a BFS error happens... although in that case, lockdep should
stop working so messing up with the graph lock may not hurt anything,
but still, I don't think we want to do that.
So probably you can open-code __lockdep_count_forward_deps() into
lockdep_count_forwards_deps(), and call print_bfs_bug() or
graph_unlock() accordingly. The body of __lockdep_count_forward_deps()
is really small, so I think it's OK to open-code it into its caller.
Regards,
Boqun
>
> return count;
> }
> @@ -2053,8 +2057,12 @@ static unsigned long __lockdep_count_backward_deps(struct lock_list *this)
> {
> unsigned long count = 0;
> struct lock_list *target_entry;
> + enum bfs_result ret;
> +
> + ret = __bfs_backwards(this, (void *)&count, noop_count, NULL, &target_entry);
>
> - __bfs_backwards(this, (void *)&count, noop_count, NULL, &target_entry);
> + if (bfs_error(ret))
> + print_bfs_bug(ret);
>
> return count;
> }
> --
> 2.30.2
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 3/3] locking/lockdep: print possible warning after counting deps
2021-06-17 15:12 ` Boqun Feng
@ 2021-06-18 1:54 ` Xiongwei Song
0 siblings, 0 replies; 6+ messages in thread
From: Xiongwei Song @ 2021-06-18 1:54 UTC (permalink / raw)
To: Boqun Feng
Cc: Xiongwei Song, peterz, mingo, will, longman, Linux Kernel Mailing List
On Thu, Jun 17, 2021 at 11:13 PM Boqun Feng <boqun.feng@gmail.com> wrote:
>
> Hi,
>
> On Thu, Jun 17, 2021 at 10:28:28PM +0800, Xiongwei Song wrote:
> > From: Xiongwei Song <sxwjean@gmail.com>
> >
> > The graph walk might hit error when counting dependencies. Once the
> > return value is negative, print a warning to reminder users.
> >
>
> Thanks for the improvement, but please see below:
>
> > Suggested-by: Waiman Long <longman@redhat.com>
> > Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
> > ---
> > kernel/locking/lockdep.c | 12 ++++++++++--
> > 1 file changed, 10 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> > index cb94097014d8..cfe0f4374594 100644
> > --- a/kernel/locking/lockdep.c
> > +++ b/kernel/locking/lockdep.c
> > @@ -2028,8 +2028,12 @@ static unsigned long __lockdep_count_forward_deps(struct lock_list *this)
> > {
> > unsigned long count = 0;
> > struct lock_list *target_entry;
> > + enum bfs_result ret;
> > +
> > + ret = __bfs_forwards(this, (void *)&count, noop_count, NULL, &target_entry);
> >
> > - __bfs_forwards(this, (void *)&count, noop_count, NULL, &target_entry);
> > + if (bfs_error(ret))
> > + print_bfs_bug(ret);
>
> Here print_bfs_bug() will eventually call debug_locks_off_graph_unlock()
> to release the graph lock, and the caller (lockdep_count_fowards_deps())
> will also call graph_unlock() afterwards, and that means we unlock
> *twice* if a BFS error happens... although in that case, lockdep should
> stop working so messing up with the graph lock may not hurt anything,
> but still, I don't think we want to do that.
>
> So probably you can open-code __lockdep_count_forward_deps() into
> lockdep_count_forwards_deps(), and call print_bfs_bug() or
> graph_unlock() accordingly. The body of __lockdep_count_forward_deps()
> is really small, so I think it's OK to open-code it into its caller.
Thank you so much for the detailed comments. Let me improve and update
the patch.
Regards,
Xiongwei
>
> Regards,
> Boqun
>
> >
> > return count;
> > }
> > @@ -2053,8 +2057,12 @@ static unsigned long __lockdep_count_backward_deps(struct lock_list *this)
> > {
> > unsigned long count = 0;
> > struct lock_list *target_entry;
> > + enum bfs_result ret;
> > +
> > + ret = __bfs_backwards(this, (void *)&count, noop_count, NULL, &target_entry);
> >
> > - __bfs_backwards(this, (void *)&count, noop_count, NULL, &target_entry);
> > + if (bfs_error(ret))
> > + print_bfs_bug(ret);
> >
> > return count;
> > }
> > --
> > 2.30.2
> >
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-06-18 1:55 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2021-06-17 14:28 [PATCH 0/3] some improvements for lockdep Xiongwei Song
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2021-06-17 14:28 ` [PATCH 2/3] locking/lockdep: unlikely conditons about BFS_RMATCH Xiongwei Song
2021-06-17 14:28 ` [PATCH 3/3] locking/lockdep: print possible warning after counting deps Xiongwei Song
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