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2017-04-19block: Make writeback throttling defaults consistent for SQ devicesJan Kara1-0/+4
When CFQ is used as an elevator, it disables writeback throttling because they don't play well together. Later when a different elevator is chosen for the device, writeback throttling doesn't get enabled again as it should. Make sure CFQ enables writeback throttling (if it should be enabled by default) when we switch from it to another IO scheduler. Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-28block: track request size in blk_issue_statShaohua Li1-5/+5
Currently there is no way to know the request size when the request is finished. Next patch will need this info. We could add extra field to record the size, but blk_issue_stat has enough space to record it, so this patch just overloads blk_issue_stat. With this, we will have 49bits to track time, which still is very long time. Signed-off-by: Shaohua Li <shli@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21blk-stat: convert to callback-based statistics reportingOmar Sandoval1-1/+1
Currently, statistics are gathered in ~0.13s windows, and users grab the statistics whenever they need them. This is not ideal for both in-tree users: 1. Writeback throttling wants its own dynamically sized window of statistics. Since the blk-stats statistics are reset after every window and the wbt windows don't line up with the blk-stats windows, wbt doesn't see every I/O. 2. Polling currently grabs the statistics on every I/O. Again, depending on how the window lines up, we may miss some I/Os. It's also unnecessary overhead to get the statistics on every I/O; the hybrid polling heuristic would be just as happy with the statistics from the previous full window. This reworks the blk-stats infrastructure to be callback-based: users register a callback that they want called at a given time with all of the statistics from the window during which the callback was active. Users can dynamically bucketize the statistics. wbt and polling both currently use read vs. write, but polling can be extended to further subdivide based on request size. The callbacks are kept on an RCU list, and each callback has percpu stats buffers. There will only be a few users, so the overhead on the I/O completion side is low. The stats flushing is also simplified considerably: since the timer function is responsible for clearing the statistics, we don't have to worry about stale statistics. wbt is a trivial conversion. After the conversion, the windowing problem mentioned above is fixed. For polling, we register an extra callback that caches the previous window's statistics in the struct request_queue for the hybrid polling heuristic to use. Since we no longer have a single stats buffer for the request queue, this also removes the sysfs and debugfs stats entries. To replace those, we add a debugfs entry for the poll statistics. Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-28blk-wbt: allow wbt to be enabled always through sysfsJens Axboe1-0/+11
Currently there's no way to enable wbt if it's not enabled in the kernel config by default for a device. Allow a write to the 'wbt_lat_usec' queue sysfs file to enable wbt. This is useful for both the kernel config case, but also if the device is CFQ managed and it was turned off by default. Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-28blk-wbt: cleanup disable-by-default for CFQJens Axboe1-2/+2
Make it clear that we are disabling wbt for the specified queued, if it was enabled by default. This is in preparation for allowing users to re-enable wbt, and not have it disabled automatically again. Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-28blk-wbt: allow reset of default latency through sysfsJens Axboe1-0/+6
Allow a write of '-1' to reset the default latency target for a given device. This removes knowledge of the different default settings for rotational vs non-rotational from user space. Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-11blk-wbt: remove stat opsJens Axboe1-11/+2
Again a leftover from when the throttling code was generic. Now that we just have the block user, get rid of the stat ops and indirections. Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-11blk-wbt: store queue instead of bdiJens Axboe1-3/+1
The bdi was a leftover from when the code was block layer agnostic. Now that we just support a block layer user, store the queue directly. Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-10blk-wbt: add general throttling mechanismJens Axboe1-0/+165
We can hook this up to the block layer, to help throttle buffered writes. wbt registers a few trace points that can be used to track what is happening in the system: wbt_lat: 259:0: latency 2446318 wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1, wmean=518866, wmin=15522, wmax=5330353, wsamples=57 wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32 This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat dumps the current read/write stats for that window, and wbt_step shows a step down event where we now scale back writes. Each trace includes the device, 259:0 in this case. Signed-off-by: Jens Axboe <axboe@fb.com>