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2017-10-10blk-stat: delete useless codeShaohua Li1-38/+7
Fix two issues: - the per-cpu stat flush is unnecessary, nobody uses per-cpu stat except sum it to global stat. We can do the calculation there. The flush just wastes cpu time. - some fields are signed int/s64. I don't see the point. Reviewed-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Shaohua Li <shli@fb.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-05-10blk-stat: don't use this_cpu_ptr() in a preemptable sectionJens Axboe1-7/+10
If PREEMPT_RCU is enabled, rcu_read_lock() isn't strong enough for us to use this_cpu_ptr() in that section. Use the safer get/put_cpu_ptr() variants instead. Reported-by: Mike Galbraith <efault@gmx.de> Fixes: 34dbad5d26e2 ("blk-stat: convert to callback-based statistics reporting") Signed-off-by: Jens Axboe <axboe@fb.com>
2017-04-21blk-stat: kill blk_stat_rq_ddir()Jens Axboe1-6/+0
No point in providing and exporting this helper. There's just one (real) user of it, just use rq_data_dir(). Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
2017-04-20blk-stat: convert blk-stat bucket callback to signedStephen Bates1-2/+4
In order to allow for filtering of IO based on some other properties of the request than direction we allow the bucket function to return an int. If the bucket callback returns a negative do no count it in the stats accumulation. Signed-off-by: Stephen Bates <sbates@raithlin.com> Fixed up Kyber scheduler stat callback. Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-28blk-throttle: add a mechanism to estimate IO latencyShaohua Li1-1/+14
User configures latency target, but the latency threshold for each request size isn't fixed. For a SSD, the IO latency highly depends on request size. To calculate latency threshold, we sample some data, eg, average latency for request size 4k, 8k, 16k, 32k .. 1M. The latency threshold of each request size will be the sample latency (I'll call it base latency) plus latency target. For example, the base latency for request size 4k is 80us and user configures latency target 60us. The 4k latency threshold will be 80 + 60 = 140us. To sample data, we calculate the order base 2 of rounded up IO sectors. If the IO size is bigger than 1M, it will be accounted as 1M. Since the calculation does round up, the base latency will be slightly smaller than actual value. Also if there isn't any IO dispatched for a specific IO size, we will use the base latency of smaller IO size for this IO size. But we shouldn't sample data at any time. The base latency is supposed to be latency where disk isn't congested, because we use latency threshold to schedule IOs between cgroups. If disk is congested, the latency is higher, using it for scheduling is meaningless. Hence we only do the sampling when block throttling is in the LOW limit, with assumption disk isn't congested in such state. If the assumption isn't true, eg, low limit is too high, calculated latency threshold will be higher. Hard disk is completely different. Latency depends on spindle seek instead of request size. Currently this feature is SSD only, we probably can use a fixed threshold like 4ms for hard disk though. Signed-off-by: Shaohua Li <shli@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21block: fix stacked driver stats init and freeJens Axboe1-1/+2
If a driver allocates a queue for stacked usage, then it does not currently get stats allocated. This causes the later init of, eg, writeback throttling to blow up. Move the init to the queue allocation instead. Additionally, allow a NULL callback unregistration. This avoids having the caller check for that, fixing another oops on removal of a block device that doesn't have poll stats allocated. Fixes: 34dbad5d26e2 ("blk-stat: convert to callback-based statistics reporting") Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21blk-stat: convert to callback-based statistics reportingOmar Sandoval1-164/+147
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>
2017-03-21blk-stat: move BLK_RQ_STAT_BATCH definition to blk-stat.cOmar Sandoval1-0/+2
This is an implementation detail that no-one outside of blk-stat.c uses. Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21blk-stat: use READ and WRITE instead of BLK_STAT_{READ,WRITE}Omar Sandoval1-41/+39
The stats buckets will become generic soon, so make the existing users use the common READ and WRITE definitions instead of one internal to blk-stat. Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21blk-stat: fix blk_stat_sum() if all samples are batchedOmar Sandoval1-2/+2
We need to flush the batch _before_ we check the number of samples, otherwise we'll miss all of the batched samples. Fixes: cf43e6b ("block: add scalable completion tracking of requests") Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-12-09blk-stat: fix a few cases of missing batch flushingJens Axboe1-0/+8
Everytime we need to read ->nr_samples, we should have flushed the batch first. The non-mq read path also needs to flush the batch. Signed-off-by: Jens Axboe <axboe@fb.com>
2016-12-02blk-stat: fix a typoShaohua Li1-1/+1
Signed-off-by: Shaohua Li <shli@fb.com> Fixes: cf43e6be865a ("block: add scalable completion tracking of requests") Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-10block: add scalable completion tracking of requestsJens Axboe1-0/+248
For legacy block, we simply track them in the request queue. For blk-mq, we track them on a per-sw queue basis, which we can then sum up through the hardware queues and finally to a per device state. The stats are tracked in, roughly, 0.1s interval windows. Add sysfs files to display the stats. The feature is off by default, to avoid any extra overhead. In-kernel users of it can turn it on by setting QUEUE_FLAG_STATS in the queue flags. We currently don't turn it on if someone just reads any of the stats files, that is something we could add as well. Signed-off-by: Jens Axboe <axboe@fb.com>