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| author | Zhiguo Niu <zhiguo.niu@unisoc.com> | 2023-08-03 14:12:42 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2023-09-13 10:42:42 +0300 |
| commit | 9183c4fe9141e6575c801aad2d9fa23b4855d763 (patch) | |
| tree | 3d1fd094b7b7f9d36b2a5d422d70e06b9971f94a /block | |
| parent | 9ca08adb75fb40a8f742c371927ee73f9dc753bf (diff) | |
| download | linux-9183c4fe9141e6575c801aad2d9fa23b4855d763.tar.xz | |
block/mq-deadline: use correct way to throttling write requests
[ Upstream commit d47f9717e5cfd0dd8c0ba2ecfa47c38d140f1bb6 ]
The original formula was inaccurate:
dd->async_depth = max(1UL, 3 * q->nr_requests / 4);
For write requests, when we assign a tags from sched_tags,
data->shallow_depth will be passed to sbitmap_find_bit,
see the following code:
nr = sbitmap_find_bit_in_word(&sb->map[index],
min_t (unsigned int,
__map_depth(sb, index),
depth),
alloc_hint, wrap);
The smaller of data->shallow_depth and __map_depth(sb, index)
will be used as the maximum range when allocating bits.
For a mmc device (one hw queue, deadline I/O scheduler):
q->nr_requests = sched_tags = 128, so according to the previous
calculation method, dd->async_depth = data->shallow_depth = 96,
and the platform is 64bits with 8 cpus, sched_tags.bitmap_tags.sb.shift=5,
sb.maps[]=32/32/32/32, 32 is smaller than 96, whether it is a read or
a write I/O, tags can be allocated to the maximum range each time,
which has not throttling effect.
In addition, refer to the methods of bfg/kyber I/O scheduler,
limit ratiois are calculated base on sched_tags.bitmap_tags.sb.shift.
This patch can throttle write requests really.
Fixes: 07757588e507 ("block/mq-deadline: Reserve 25% of scheduler tags for synchronous requests")
Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/1691061162-22898-1-git-send-email-zhiguo.niu@unisoc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'block')
| -rw-r--r-- | block/mq-deadline.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/block/mq-deadline.c b/block/mq-deadline.c index f10c2a0d18d4..55e26065c2e2 100644 --- a/block/mq-deadline.c +++ b/block/mq-deadline.c @@ -622,8 +622,9 @@ static void dd_depth_updated(struct blk_mq_hw_ctx *hctx) struct request_queue *q = hctx->queue; struct deadline_data *dd = q->elevator->elevator_data; struct blk_mq_tags *tags = hctx->sched_tags; + unsigned int shift = tags->bitmap_tags.sb.shift; - dd->async_depth = max(1UL, 3 * q->nr_requests / 4); + dd->async_depth = max(1U, 3 * (1U << shift) / 4); sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, dd->async_depth); } |