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Wed, 16 Jun 2021 07:48:59 -0700 (PDT) Received: from llong.remote.csb ([2601:191:8500:76c0::cdbc]) by smtp.gmail.com with ESMTPSA id y189sm2057298wmy.25.2021.06.16.07.48.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Jun 2021 07:48:59 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Subject: Re: [PATCH] locking/lockdep: unlikely bfs error check To: Xiongwei Song , peterz@infradead.org, mingo@redhat.com, will@kernel.org, boqun.feng@gmail.com Cc: linux-kernel@vger.kernel.org, Xiongwei Song References: <20210616144210.278662-1-sxwjean@me.com> Message-ID: Date: Wed, 16 Jun 2021 10:48:56 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <20210616144210.278662-1-sxwjean@me.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/16/21 10:42 AM, Xiongwei Song wrote: > From: Xiongwei Song > > The error from graph walk is small probability event, so unlikely > bfs_error can improve performance a little bit. > > Signed-off-by: Xiongwei Song > --- > 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 -> 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. Cheers, Longman