• Javier González's avatar
    lightnvm: pblk: sched. metadata on write thread · dd2a4343
    Javier González authored
    At the moment, line metadata is persisted on a separate work queue, that
    is kicked each time that a line is closed. The assumption when designing
    this was that freeing the write thread from creating a new write request
    was better than the potential impact of writes colliding on the media
    (user I/O and metadata I/O). Experimentation has proven that this
    assumption is wrong; collision can cause up to 25% of bandwidth and
    introduce long tail latencies on the write thread, which potentially
    cause user write threads to spend more time spinning to get a free entry
    on the write buffer.
    
    This patch moves the metadata logic to the write thread. When a line is
    closed, remaining metadata is written in memory and is placed on a
    metadata queue. The write thread then takes the metadata corresponding
    to the previous line, creates the write request and schedules it to
    minimize collisions on the media. Using this approach, we see that we
    can saturate the media's bandwidth, which helps reducing both write
    latencies and the spinning time for user writer threads.
    Signed-off-by: default avatarJavier González <javier@cnexlabs.com>
    Signed-off-by: default avatarMatias Bjørling <matias@cnexlabs.com>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    dd2a4343
pblk-map.c 4.68 KB