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From:   zhuxiaohui <zhuxiaohui400@gmail.com>
To:     tj@kernel.org, josef@toxicpanda.com, axboe@kernel.dk
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        cgroups@vger.kernel.org, zhuxiaohui <zhuxiaohui.400@bytedance.com>
Subject: [PATCH 1/1] blk-throttle: fix throttle configuring not effective
Date:   Sat, 12 Aug 2023 15:21:16 +0800
Message-ID: <20230812072116.42321-1-zhuxiaohui.400@bytedance.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

when updating block throttle limit with persistence and stable io
pressure, especially a relative high io pressure, fio test e.g.,
there may never be a change to start a new slice, and carryover_ios &
carryover_bytes will not be cleared.

As a result, when reconfiguring block throttle limit, we can notice that
the actual iops and throughput is a random value far away from what is
set

So we need to update carryover value when dispatching bio

Signed-off-by: zhuxiaohui <zhuxiaohui.400@bytedance.com>
---
 block/blk-throttle.c | 26 ++++++++++++++++++++++++++
 block/blk-throttle.h |  4 ++--
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 7397ff199d66..13c9d87a7201 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -821,6 +821,30 @@ static void tg_update_carryover(struct throtl_grp *tg)
 		   tg->carryover_ios[READ], tg->carryover_ios[WRITE]);
 }
 
+static void tg_charge_carryover(struct throtl_grp *tg, struct bio *bio)
+{
+	bool rw = bio_data_dir(bio);
+
+	if (unlikely(tg->carryover_bytes[rw])) {
+		unsigned int bio_size = throtl_bio_data_size(bio);
+		unsigned int carryout_size = abs(tg->carryover_bytes[rw]);
+
+		carryout_size = min(carryout_size, bio_size);
+
+		if (tg->carryover_bytes[rw] < 0)
+			tg->carryover_bytes[rw] += carryout_size;
+		else
+			tg->carryover_bytes[rw] -= carryout_size;
+	}
+
+	if (unlikely(tg->carryover_ios[rw])) {
+		if (tg->carryover_ios[rw] < 0)
+			tg->carryover_ios[rw] += 1;
+		else
+			tg->carryover_ios[rw] -= 1;
+	}
+}
+
 static unsigned long tg_within_iops_limit(struct throtl_grp *tg, struct bio *bio,
 				 u32 iops_limit)
 {
@@ -965,6 +989,8 @@ static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio)
 
 	tg->io_disp[rw]++;
 	tg->last_io_disp[rw]++;
+
+	tg_charge_carryover(tg, bio);
 }
 
 /**
diff --git a/block/blk-throttle.h b/block/blk-throttle.h
index d1ccbfe9f797..8f1642becb23 100644
--- a/block/blk-throttle.h
+++ b/block/blk-throttle.h
@@ -127,8 +127,8 @@ struct throtl_grp {
 	 * bytes/ios are waited already in previous configuration, and they will
 	 * be used to calculate wait time under new configuration.
 	 */
-	uint64_t carryover_bytes[2];
-	unsigned int carryover_ios[2];
+	int64_t carryover_bytes[2];
+	int carryover_ios[2];
 
 	unsigned long last_check_time;
 
-- 
2.39.2