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Wed, 16 Jun 2021 08:11:24 -0700 (PDT) Received: from llong.remote.csb ([2601:191:8500:76c0::cdbc]) by smtp.gmail.com with ESMTPSA id s21sm3058579wmh.9.2021.06.16.08.11.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Jun 2021 08:11:23 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Subject: Re: [PATCH] locking/lockdep: unlikely bfs error check To: Xiongwei Song , Waiman Long Cc: peterz@infradead.org, mingo@redhat.com, will@kernel.org, boqun.feng@gmail.com, linux-kernel@vger.kernel.org, Xiongwei Song References: <20210616144210.278662-1-sxwjean@me.com> Message-ID: <9c60a4a9-c241-73de-57b5-c5fc45720677@redhat.com> Date: Wed, 16 Jun 2021 11:11:21 -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: 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 10:59 AM, Xiongwei Song wrote: > >> On Jun 16, 2021, at 10:48 PM, Waiman Long wrote: >> >> 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. > 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. Cheers, Longman