user/sven/linux.git/include/linux/elevator.h, branch v5.12-rc2

blk-mq: Improve performance of non-mq IO schedulers with multiple HW queues

2021-01-25T01:19:46Z

Currently when non-mq aware IO scheduler (BFQ, mq-deadline) is used for a queue with multiple HW queues, the performance it rather bad. The problem is that these IO schedulers use queue-wide locking and their dispatch function does not respect the hctx it is passed in and returns any request it finds appropriate. Thus locality of request access is broken and dispatch from multiple CPUs just contends on IO scheduler locks. For these IO schedulers there's little point in dispatching from multiple CPUs. Instead dispatch always only from a single CPU to limit contention. Below is a comparison of dbench runs on XFS filesystem where the storage is a raid card with 64 HW queues and to it attached a single rotating disk. BFQ is used as IO scheduler: clients MQ SQ MQ-Patched Amean 1 39.12 (0.00%) 43.29 * -10.67%* 36.09 * 7.74%* Amean 2 128.58 (0.00%) 101.30 * 21.22%* 96.14 * 25.23%* Amean 4 577.42 (0.00%) 494.47 * 14.37%* 508.49 * 11.94%* Amean 8 610.95 (0.00%) 363.86 * 40.44%* 362.12 * 40.73%* Amean 16 391.78 (0.00%) 261.49 * 33.25%* 282.94 * 27.78%* Amean 32 324.64 (0.00%) 267.71 * 17.54%* 233.00 * 28.23%* Amean 64 295.04 (0.00%) 253.02 * 14.24%* 242.37 * 17.85%* Amean 512 10281.61 (0.00%) 10211.16 * 0.69%* 10447.53 * -1.61%* Numbers are times so lower is better. MQ is stock 5.10-rc6 kernel. SQ is the same kernel with megaraid_sas.host_tagset_enable=0 so that the card advertises just a single HW queue. MQ-Patched is a kernel with this patch applied. You can see multiple hardware queues heavily hurt performance in combination with BFQ. The patch restores the performance. Signed-off-by: Jan Kara Reviewed-by: Ming Lei Signed-off-by: Jens Axboe

blk-mq: remove the bio argument to ->prepare_request

2020-05-29T16:23:24Z

None of the I/O schedulers actually needs it. Signed-off-by: Christoph Hellwig Reviewed-by: Ming Lei Reviewed-by: Hannes Reinecke Reviewed-by: Johannes Thumshirn Reviewed-by: Bart Van Assche Reviewed-by: Daniel Wagner Signed-off-by: Jens Axboe

block: Introduce elevator features

2019-09-06T01:52:33Z

Introduce the definition of elevator features through the elevator_features flags in the elevator_type structure. Each flag can represent a feature supported by an elevator. The first feature defined by this patch is support for zoned block device sequential write constraint with the flag ELEVATOR_F_ZBD_SEQ_WRITE, which is implemented by the mq-deadline elevator using zone write locking. Other possible features are IO priorities, write hints, latency targets or single-LUN dual-actuator disks (for which the elevator could maintain one LBA ordered list per actuator). The required_elevator_features field is also added to the request_queue structure to allow a device driver to specify elevator feature flags that an elevator must support for the correct operation of the device (e.g. device drivers for zoned block devices can have the ELEVATOR_F_ZBD_SEQ_WRITE flag as a required feature). The helper function blk_queue_required_elevator_features() is defined for setting this new field. With these two new fields in place, the elevator functions elevator_match() and elevator_find() are modified to allow a user to set only an elevator with a set of features that satisfies the device required features. Elevators not matching the device requirements are not shown in the device sysfs queue/scheduler file to prevent their use. The "none" elevator can always be selected as before. Reviewed-by: Johannes Thumshirn Reviewed-by: Christoph Hellwig Reviewed-by: Ming Lei Signed-off-by: Damien Le Moal Signed-off-by: Jens Axboe

block: blk-mq: Remove blk_mq_sched_started_request and started_request

2019-07-23T13:25:09Z

blk_mq_sched_completed_request is a function that checks if the elevator related to the request has started_request implemented, but currently, none of the available IO schedulers implement started_request, so remove both. Signed-off-by: Marcos Paulo de Souza Signed-off-by: Jens Axboe

block: Fix elevator name declaration

2019-07-10T20:18:01Z

The elevator_name field in struct elevator_type is declared as an array of characters (ELV_NAME_MAX size) but in practice used as a string pointer with its initialization done statically within each elevator elevator_type structure declaration. Change the declaration of elevator_name to the more appropriate "const char *" type. Acked-by: Marcos Paulo de Souza Signed-off-by: Damien Le Moal Signed-off-by: Jens Axboe

block: Remove unused definitions

2019-07-10T20:18:01Z

The ELV_MQUEUE_XXX definitions in include/linux/elevator.h are unused since the removal of elevator_may_queue_fn in kernel 5.0. Remove these definitions and also remove the documentation of elevator_may_queue_fn in Documentiation/block/biodoc.txt. Acked-by: Marcos Paulo de Souza Signed-off-by: Damien Le Moal Signed-off-by: Jens Axboe

block: remove the bi_phys_segments field in struct bio

2019-06-20T16:29:22Z

We only need the number of segments in the blk-mq submission path. Remove the field from struct bio, and return it from a variant of blk_queue_split instead of that it can passed as an argument to those functions that need the value. This also means we stop recounting segments except for cloning and partial segments. To keep the number of arguments in this how path down remove pointless struct request_queue arguments from any of the functions that had it and grew a nr_segs argument. Signed-off-by: Christoph Hellwig Signed-off-by: Jens Axboe

bfq: update internal depth state when queue depth changes

2019-04-14T01:08:22Z

A previous commit moved the shallow depth and BFQ depth map calculations to be done at init time, moving it outside of the hotter IO path. This potentially causes hangs if the users changes the depth of the scheduler map, by writing to the 'nr_requests' sysfs file for that device. Add a blk-mq-sched hook that allows blk-mq to inform the scheduler if the depth changes, so that the scheduler can update its internal state. Tested-by: Kai Krakow Reported-by: Paolo Valente Fixes: f0635b8a416e ("bfq: calculate shallow depths at init time") Signed-off-by: Jens Axboe

block: get rid of MQ scheduler ops union

2018-11-07T20:42:32Z

This is a remnant of when we had ops for both SQ and MQ schedulers. Now it's just MQ, so get rid of the union. Reviewed-by: Omar Sandoval Signed-off-by: Jens Axboe

block: remove dead elevator code

2018-11-07T20:42:32Z

This removes a bunch of core and elevator related code. On the core front, we remove anything related to queue running, draining, initialization, plugging, and congestions. We also kill anything related to request allocation, merging, retrieval, and completion. Remove any checking for single queue IO schedulers, as they no longer exist. This means we can also delete a bunch of code related to request issue, adding, completion, etc - and all the SQ related ops and helpers. Also kill the load_default_modules(), as all that did was provide for a way to load the default single queue elevator. Tested-by: Ming Lei Reviewed-by: Omar Sandoval Signed-off-by: Jens Axboe