blk-mq: introduce new queue attribute async_depth#536
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This value represents the number of requests for elevator tags, or drivers tags if elevator is none. The max value for elevator tags is 2048, and in drivers at most 16 bits is used for tag. Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> Reviewed-by: Hannes Reinecke <hare@suse.de>
bfq and mq-deadline consider sync writes as async requests and only reserve tags for sync reads by async_depth, however, kyber doesn't consider sync writes as async requests for now. Consider the case there are lots of dirty pages, and user use fsync to flush dirty pages. In this case sched_tags can be exhausted by sync writes and sync reads can stuck waiting for tag. Hence let kyber follow what mq-deadline and bfq did, and unify async requests checking for all elevators. Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> Reviewed-by: Hannes Reinecke <hare@suse.de>
There are no functional changes, just make code cleaner. Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Hannes Reinecke <hare@suse.de>
Add a new field async_depth to request_queue and related APIs, this is currently not used, following patches will convert elevators to use this instead of internal async_depth. Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> Reviewed-by: Hannes Reinecke <hare@suse.de>
Instead of the internal async_depth, remove kqd->async_depth and related helpers. Noted elevator attribute async_depth is now removed, queue attribute with the same name is used instead. Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> Reviewed-by: Hannes Reinecke <hare@suse.de>
In downstream kernel, we test with mq-deadline with many fio workloads, and we found a performance regression after commit 39823b4 ("block/mq-deadline: Fix the tag reservation code") with following test: [global] rw=randread direct=1 ramp_time=1 ioengine=libaio iodepth=1024 numjobs=24 bs=1024k group_reporting=1 runtime=60 [job1] filename=/dev/sda Root cause is that mq-deadline now support configuring async_depth, although the default value is nr_request, however the minimal value is 1, hence min_shallow_depth is set to 1, causing wake_batch to be 1. For consequence, sbitmap_queue will be waken up after each IO instead of 8 IO. In this test case, sda is HDD and max_sectors is 128k, hence each submitted 1M io will be splited into 8 sequential 128k requests, however due to there are 24 jobs and total tags are exhausted, the 8 requests are unlikely to be dispatched sequentially, and changing wake_batch to 1 will make this much worse, accounting blktrace D stage, the percentage of sequential io is decreased from 8% to 0.8%. Fix this problem by converting to request_queue->async_depth, where min_shallow_depth is set each time async_depth is updated. Noted elevator attribute async_depth is now removed, queue attribute with the same name is used instead. Fixes: 39823b4 ("block/mq-deadline: Fix the tag reservation code") Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> Reviewed-by: Bart Van Assche <bvanassche@acm.org> Reviewed-by: Hannes Reinecke <hare@suse.de>
The default limits is unchanged, and user can configure async_depth now. Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> Reviewed-by: Hannes Reinecke <hare@suse.de>
Explain the attribute and the default value in different case. Signed-off-by: Yu Kuai <yukuai@fnnas.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
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Pull request for series with
subject: blk-mq: introduce new queue attribute async_depth
version: 7
url: https://patchwork.kernel.org/project/linux-block/list/?series=1050157