6.4-stable review patch. If anyone has any objections, please let me know.
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From: Zhiguo Niu zhiguo.niu@unisoc.com
[ 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@uniso... Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/mq-deadline.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/block/mq-deadline.c b/block/mq-deadline.c index 5839a027e0f05..7e043d4a78f84 100644 --- a/block/mq-deadline.c +++ b/block/mq-deadline.c @@ -620,8 +620,9 @@ 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); }