Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210616144210.278662-1-sxwjean@me.com> <a341e1f1-39a5-dca3-9454-8eabe085928b@redhat.com>
 <BF7CB29B-0B34-4462-B793-732C1EF9DC40@me.com> <9c60a4a9-c241-73de-57b5-c5fc45720677@redhat.com>
In-Reply-To: <9c60a4a9-c241-73de-57b5-c5fc45720677@redhat.com>
From:   Xiongwei Song <sxwjean@gmail.com>
Date:   Thu, 17 Jun 2021 10:14:11 +0800
Message-ID: <CAEVVKH_nN65D6AnJbOceSAh1ttbH+eQpb9ycGxPoYYGGnM_LwA@mail.gmail.com>
Subject: Re: [PATCH] locking/lockdep: unlikely bfs error check
To:     Waiman Long <llong@redhat.com>
Cc:     Xiongwei Song <sxwjean@me.com>, peterz@infradead.org,
        mingo@redhat.com, will@kernel.org,
        Boqun Feng <boqun.feng@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, Jun 16, 2021 at 11:11 PM Waiman Long <llong@redhat.com> wrote:
>
> On 6/16/21 10:59 AM, Xiongwei Song wrote:
> >
> >> On Jun 16, 2021, at 10:48 PM, Waiman Long <llong@redhat.com> wrote:
> >>
> >> On 6/16/21 10:42 AM, Xiongwei Song wrote:
> >>> From: Xiongwei Song <sxwjean@gmail.com>
> >>>
> >>> The error from graph walk is small probability event, so unlikely
> >>> bfs_error can improve performance a little bit.
> >>>
> >>> Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
> >>> ---
> >>>   kernel/locking/lockdep.c | 12 ++++++------
> >>>   1 file changed, 6 insertions(+), 6 deletions(-)
> >>>
> >>> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> >>> index 074fd6418c20..af8c9203cd3e 100644
> >>> --- a/kernel/locking/lockdep.c
> >>> +++ b/kernel/locking/lockdep.c
> >>> @@ -2646,7 +2646,7 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
> >>>     bfs_init_rootb(&this, prev);
> >>>             ret = __bfs_backwards(&this, &usage_mask, usage_accumulate, usage_skip, NULL);
> >>> -   if (bfs_error(ret)) {
> >>> +   if (unlikely(bfs_error(ret))) {
> >>>             print_bfs_bug(ret);
> >>>             return 0;
> >>>     }
> >>> @@ -2664,7 +2664,7 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
> >>>     bfs_init_root(&that, next);
> >>>             ret = find_usage_forwards(&that, forward_mask, &target_entry1);
> >>> -   if (bfs_error(ret)) {
> >>> +   if (unlikely(bfs_error(ret))) {
> >>>             print_bfs_bug(ret);
> >>>             return 0;
> >>>     }
> >>> @@ -2679,7 +2679,7 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
> >>>     backward_mask = original_mask(target_entry1->class->usage_mask);
> >>>             ret = find_usage_backwards(&this, backward_mask, &target_entry);
> >>> -   if (bfs_error(ret)) {
> >>> +   if (unlikely(bfs_error(ret))) {
> >>>             print_bfs_bug(ret);
> >>>             return 0;
> >>>     }
> >>> @@ -2998,7 +2998,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
> >>>      * Is the <prev> -> <next> link redundant?
> >>>      */
> >>>     ret = check_redundant(prev, next);
> >>> -   if (bfs_error(ret))
> >>> +   if (unlikely(bfs_error(ret)))
> >>>             return 0;
> >>>     else if (ret == BFS_RMATCH)
> >>>             return 2;
> >>> @@ -3911,7 +3911,7 @@ check_usage_forwards(struct task_struct *curr, struct held_lock *this,
> >>>             bfs_init_root(&root, this);
> >>>     ret = find_usage_forwards(&root, usage_mask, &target_entry);
> >>> -   if (bfs_error(ret)) {
> >>> +   if (unlikely(bfs_error(ret))) {
> >>>             print_bfs_bug(ret);
> >>>             return 0;
> >>>     }
> >>> @@ -3946,7 +3946,7 @@ check_usage_backwards(struct task_struct *curr, struct held_lock *this,
> >>>             bfs_init_rootb(&root, this);
> >>>     ret = find_usage_backwards(&root, usage_mask, &target_entry);
> >>> -   if (bfs_error(ret)) {
> >>> +   if (unlikely(bfs_error(ret))) {
> >>>             print_bfs_bug(ret);
> >>>             return 0;
> >>>     }
> >> I think it is better to put the unlikely() directly into the bfs_error() inline function instead of sprinkling it all over the place.
> > Sounds good. Thank you for the suggestion. I will update the patch.
>
> Another nit. It is a bit odd that sent out two patches separately though
> they do seem to have a bit of dependency. I think you should post them
> as a 2-patch series.

Ok. Let me do it. Thank you again.

Regards,
Xiongwei

> Cheers,
> Longman
>