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[2.35.55.161]) by smtp.gmail.com with ESMTPSA id d27-20020a170906305b00b0073d71792c8dsm1666088ejd.180.2022.10.30.03.03.42 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sun, 30 Oct 2022 03:03:42 -0700 (PDT) From: Paolo Valente To: Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Davide Zini , Paolo Valente Subject: [PATCH V5 8/8] block, bfq: balance I/O injection among underutilized actuators Date: Sun, 30 Oct 2022 11:03:00 +0100 Message-Id: <20221030100300.3085-9-paolo.valente@linaro.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20221030100300.3085-1-paolo.valente@linaro.org> References: <20221030100300.3085-1-paolo.valente@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Davide Zini Upon the invocation of its dispatch function, BFQ returns the next I/O request of the in-service bfq_queue, unless some exception holds. One such exception is that there is some underutilized actuator, different from the actuator for which the in-service queue contains I/O, and that some other bfq_queue happens to contain I/O for such an actuator. In this case, the next I/O request of the latter bfq_queue, and not of the in-service bfq_queue, is returned (I/O is injected from that bfq_queue). To find such an actuator, a linear scan, in increasing index order, is performed among actuators. Performing a linear scan entails a prioritization among actuators: an underutilized actuator may be considered for injection only if all actuators with a lower index are currently fully utilized, or if there is no pending I/O for any lower-index actuator that happens to be underutilized. This commits breaks this prioritization and tends to distribute injection uniformly across actuators. This is obtained by adding the following condition to the linear scan: even if an actuator A is underutilized, A is however skipped if its load is higher than that of the next actuator. Signed-off-by: Paolo Valente Signed-off-by: Davide Zini --- block/bfq-iosched.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index c9af17a36219..77002ebcab39 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -4822,10 +4822,16 @@ bfq_find_active_bfqq_for_actuator(struct bfq_data *bfqd, /* * Perform a linear scan of each actuator, until an actuator is found - * for which the following two conditions hold: the load of the - * actuator is below the threshold (see comments on actuator_load_threshold - * for details), and there is a queue that contains I/O for that - * actuator. On success, return that queue. + * for which the following three conditions hold: the load of the + * actuator is below the threshold (see comments on + * actuator_load_threshold for details) and lower than that of the + * next actuator (comments on this extra condition below), and there + * is a queue that contains I/O for that actuator. On success, return + * that queue. + * + * Performing a plain linear scan entails a prioritization among + * actuators. The extra condition above breaks this prioritization and + * tends to distribute injection uniformly across actuators. */ static struct bfq_queue * bfq_find_bfqq_for_underused_actuator(struct bfq_data *bfqd) @@ -4833,7 +4839,9 @@ bfq_find_bfqq_for_underused_actuator(struct bfq_data *bfqd) int i; for (i = 0 ; i < bfqd->num_actuators; i++) - if (bfqd->rq_in_driver[i] < bfqd->actuator_load_threshold) { + if (bfqd->rq_in_driver[i] < bfqd->actuator_load_threshold && + (i == bfqd->num_actuators - 1 || + bfqd->rq_in_driver[i] < bfqd->rq_in_driver[i+1])) { struct bfq_queue *bfqq = bfq_find_active_bfqq_for_actuator(bfqd, i); -- 2.20.1