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authorJosef Bacik <josef@toxicpanda.com>2018-09-28 19:45:42 +0200
committerJens Axboe <axboe@kernel.dk>2018-09-28 19:47:31 +0200
commit1fa2840e56f9032e14a75fcf67edfe0f21102e4b (patch)
tree8a4fa641b207b2dd864cd62302ccb91f582ec74e /block/bio.c
parentblk-iolatency: deal with small samples (diff)
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blk-iolatency: use a percentile approache for ssd's
We use an average latency approach for determining if we're missing our latency target. This works well for rotational storage where we have generally consistent latencies, but for ssd's and other low latency devices you have more of a spikey behavior, which means we often won't throttle misbehaving groups because a lot of IO completes at drastically faster times than our latency target. Instead keep track of how many IO's miss our target and how many IO's are done in our time window. If the p(90) latency is above our target then we know we need to throttle. With this change in place we are seeing the same throttling behavior with our testcase on ssd's as we see with rotational drives. Signed-off-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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