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2016-09-19sbitmap: initialize weight to zeroColin Ian King1-1/+1
Variable weight is not being initialized to zero before it is used to compute the weight sum. Ensure it is initialized to zero. Found with static analysis with cppcheck: [lib/sbitmap.c:177]: (error) Uninitialized variable: weight Signed-off-by: Colin Ian King <colin.king@canonical.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-09-17sbitmap: don't update the allocation hint on clear after resizeOmar Sandoval1-1/+1
If we have a bunch of high-numbered bits allocated and then we resize the struct sbitmap_queue, when those bits get cleared, we'll update the hint and then have to re-randomize it repeatedly. Avoid that by checking that the cleared bit is still a valid hint. No measurable performance difference in the common case. Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-09-17sbitmap: re-initialize allocation hints after resizeOmar Sandoval1-2/+7
After a struct sbitmap_queue is resized smaller, the allocation hints may still be set to bits beyond the new depth of the bitmap. This means that, for example, if the number of blk-mq tags is reduced through sysfs, more requests than the nominal queue depth may be in flight. It's tempting to fix this at resize time by doing a one-time reinitialization of the hints, but this can race with __sbitmap_queue_get() updating the hint. Instead, check the hint before we use it. This caused no measurable performance difference in my synthetic benchmarks. Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-09-17sbitmap: randomize initial alloc_hint valuesOmar Sandoval1-0/+6
In order to get good cache behavior from a sbitmap, we want each CPU to stick to its own cacheline(s) as much as possible. This might happen naturally as the bitmap gets filled up and the alloc_hint values spread out, but we really want this behavior from the start. blk-mq apparently intended to do this, but the code to do this was never wired up. Get rid of the dead code and make it part of the sbitmap library. Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-09-17sbitmap: push alloc policy into sbitmap_queueOmar Sandoval1-6/+8
Again, there's no point in passing this in every time. Make it part of struct sbitmap_queue and clean up the API. Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-09-17sbitmap: push per-cpu last_tag into sbitmap_queueOmar Sandoval1-1/+34
Allocating your own per-cpu allocation hint separately makes for an awkward API. Instead, allocate the per-cpu hint as part of the struct sbitmap_queue. There's no point for a struct sbitmap_queue without the cache, but you can still use a bare struct sbitmap. Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-09-17sbitmap: allocate wait queues on a specific nodeOmar Sandoval1-1/+1
The original bt_alloc() we converted from was using kzalloc(), not kzalloc_node(), to allocate the wait queues. This was probably an oversight, so fix it for sbitmap_queue_init_node(). Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-09-17blk-mq: abstract tag allocation out into sbitmap libraryOmar Sandoval1-0/+301
This is a generally useful data structure, so make it available to anyone else who might want to use it. It's also a nice cleanup separating the allocation logic from the rest of the tag handling logic. The code is behind a new Kconfig option, CONFIG_SBITMAP, which is only selected by CONFIG_BLOCK for now. This should be a complete noop functionality-wise. Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>