• Omar Sandoval's avatar
    blk-mq: introduce Kyber multiqueue I/O scheduler · 00e04393
    Omar Sandoval authored
    The Kyber I/O scheduler is an I/O scheduler for fast devices designed to
    scale to multiple queues. Users configure only two knobs, the target
    read and synchronous write latencies, and the scheduler tunes itself to
    achieve that latency goal.
    The implementation is based on "tokens", built on top of the scalable
    bitmap library. Tokens serve as a mechanism for limiting requests. There
    are two tiers of tokens: queueing tokens and dispatch tokens.
    A queueing token is required to allocate a request. In fact, these
    tokens are actually the blk-mq internal scheduler tags, but the
    scheduler manages the allocation directly in order to implement its
    Dispatch tokens are device-wide and split up into two scheduling
    domains: reads vs. writes. Each hardware queue dispatches batches
    round-robin between the scheduling domains as long as tokens are
    available for that domain.
    These tokens can be used as the mechanism to enable various policies.
    The policy Kyber uses is inspired by active queue management techniques
    for network routing, similar to blk-wbt. The scheduler monitors
    latencies and scales the number of dispatch tokens accordingly. Queueing
    tokens are used to prevent starvation of synchronous requests by
    asynchronous requests.
    Various extensions are possible, including better heuristics and ionice
    support. The new scheduler isn't set as the default yet.
    Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
    Signed-off-by: default avatarJens Axboe <axboe@fb.com>
kyber-iosched.txt 392 Bytes