pm24.git/include/linux/blk_types.h, branch v4.12

block: add a REQ_NOUNMAP flag for REQ_OP_WRITE_ZEROES

2017-04-08T17:25:38Z

If this flag is set logical provisioning capable device should release space for the zeroed blocks if possible, if it is not set devices should keep the blocks anchored. Also remove an out of sync kerneldoc comment for a static function that would have become even more out of data with this change. Signed-off-by: Christoph Hellwig Reviewed-by: Martin K. Petersen Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

block: renumber REQ_OP_WRITE_ZEROES

2017-04-08T17:25:38Z

Make life easy for implementations that needs to send a data buffer to the device (e.g. SCSI) by numbering it as a data out command. Signed-off-by: Christoph Hellwig Reviewed-by: Martin K. Petersen Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe

block: trace completion of all bios.

2017-04-07T15:40:52Z

Currently only dm and md/raid5 bios trigger trace_block_bio_complete(). Now that we have bio_chain() and bio_inc_remaining(), it is not possible, in general, for a driver to know when the bio is really complete. Only bio_endio() knows that. So move the trace_block_bio_complete() call to bio_endio(). Now trace_block_bio_complete() pairs with trace_block_bio_queue(). Any bio for which a 'queue' event is traced, will subsequently generate a 'complete' event. There are a few cases where completion tracing is not wanted. 1/ If blk_update_request() has already generated a completion trace event at the 'request' level, there is no point generating one at the bio level too. In this case the bi_sector and bi_size will have changed, so the bio level event would be wrong 2/ If the bio hasn't actually been queued yet, but is being aborted early, then a trace event could be confusing. Some filesystems call bio_endio() but do not want tracing. 3/ The bio_integrity code interposes itself by replacing bi_end_io, then restoring it and calling bio_endio() again. This would produce two identical trace events if left like that. To handle these, we introduce a flag BIO_TRACE_COMPLETION and only produce the trace event when this is set. We address point 1 above by clearing the flag in blk_update_request(). We address point 2 above by only setting the flag when generic_make_request() is called. We address point 3 above by clearing the flag after generating a completion event. When bio_split() is used on a bio, particularly in blk_queue_split(), there is an extra complication. A new bio is split off the front, and may be handle directly without going through generic_make_request(). The old bio, which has been advanced, is passed to generic_make_request(), so it will trigger a trace event a second time. Probably the best result when a split happens is to see a single 'queue' event for the whole bio, then multiple 'complete' events - one for each component. To achieve this was can: - copy the BIO_TRACE_COMPLETION flag to the new bio in bio_split() - avoid generating a 'queue' event if BIO_TRACE_COMPLETION is already set. This way, the split-off bio won't create a queue event, the original won't either even if it re-submitted to generic_make_request(), but both will produce completion events, each for their own range. So if generic_make_request() is called (which generates a QUEUED event), then bi_endio() will create a single COMPLETE event for each range that the bio is split into, unless the driver has explicitly requested it not to. Signed-off-by: NeilBrown Signed-off-by: Jens Axboe

block: simple improvements for bio->flags

2017-04-07T15:39:29Z

The comment for the 'flags' field of 'bio' mentions "command" which is no longer stored there, and doesn't mention the bvec pool number, which is. BIO_RESET_BITS is set in such a way that it would need to be updated if new bits were added, which is easy to miss. BVEC_POOL_BITS is larger than needed. The BVEC_POOL_IDX() ranges from 0 to 6, so 3 bits are sufficient. This patch make improvements in each of these areas. Signed-off-by: NeilBrown Signed-off-by: Jens Axboe

blk-throttle: add a mechanism to estimate IO latency

2017-03-28T14:02:20Z

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 Signed-off-by: Jens Axboe

block: track request size in blk_issue_stat

2017-03-28T14:02:20Z

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 Signed-off-by: Jens Axboe

blk-throttle: add a simple idle detection

2017-03-28T14:02:20Z

A cgroup gets assigned a low limit, but the cgroup could never dispatch enough IO to cross the low limit. In such case, the queue state machine will remain in LIMIT_LOW state and all other cgroups will be throttled according to low limit. This is unfair for other cgroups. We should treat the cgroup idle and upgrade the state machine to lower state. We also have a downgrade logic. If the state machine upgrades because of cgroup idle (real idle), the state machine will downgrade soon as the cgroup is below its low limit. This isn't what we want. A more complicated case is cgroup isn't idle when queue is in LIMIT_LOW. But when queue gets upgraded to lower state, other cgroups could dispatch more IO and this cgroup can't dispatch enough IO, so the cgroup is below its low limit and looks like idle (fake idle). In this case, the queue should downgrade soon. The key to determine if we should do downgrade is to detect if cgroup is truely idle. Unfortunately it's very hard to determine if a cgroup is real idle. This patch uses the 'think time check' idea from CFQ for the purpose. Please note, the idea doesn't work for all workloads. For example, a workload with io depth 8 has disk utilization 100%, hence think time is 0, eg, not idle. But the workload can run higher bandwidth with io depth 16. Compared to io depth 16, the io depth 8 workload is idle. We use the idea to roughly determine if a cgroup is idle. We treat a cgroup idle if its think time is above a threshold (by default 1ms for SSD and 100ms for HD). The idea is think time above the threshold will start to harm performance. HD is much slower so a longer think time is ok. The patch (and the latter patches) uses 'unsigned long' to track time. We convert 'ns' to 'us' with 'ns >> 10'. This is fast but loses precision, should not a big deal. Signed-off-by: Shaohua Li Signed-off-by: Jens Axboe

blk-stat: convert to callback-based statistics reporting

2017-03-21T16:03:11Z

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 Signed-off-by: Jens Axboe

blk-stat: move BLK_RQ_STAT_BATCH definition to blk-stat.c

2017-03-21T16:03:08Z

This is an implementation detail that no-one outside of blk-stat.c uses. Signed-off-by: Omar Sandoval Signed-off-by: Jens Axboe

block: fold cmd_type into the REQ_OP_ space

2017-01-31T21:00:44Z

Instead of keeping two levels of indirection for requests types, fold it all into the operations. The little caveat here is that previously cmd_type only applied to struct request, while the request and bio op fields were set to plain REQ_OP_READ/WRITE even for passthrough operations. Instead this patch adds new REQ_OP_* for SCSI passthrough and driver private requests, althought it has to add two for each so that we can communicate the data in/out nature of the request. Signed-off-by: Christoph Hellwig Signed-off-by: Jens Axboe