• Dave Chinner's avatar
    xfs: Do background CIL flushes via a workqueue · 4c2d542f
    Dave Chinner authored
    Doing background CIL flushes adds significant latency to whatever
    async transaction that triggers it. To avoid blocking async
    transactions on things like waiting for log buffer IO to complete,
    move the CIL push off into a workqueue.  By moving the push work
    into a workqueue, we remove all the latency that the commit adds
    from the foreground transaction commit path. This also means that
    single threaded workloads won't do the CIL push procssing, leaving
    them more CPU to do more async transactions.
    
    To do this, we need to keep track of the sequence number we have
    pushed work for. This avoids having many transaction commits
    attempting to schedule work for the same sequence, and ensures that
    we only ever have one push (background or forced) in progress at a
    time. It also means that we don't need to take the CIL lock in write
    mode to check for potential background push races, which reduces
    lock contention.
    
    To avoid potential issues with "smart" IO schedulers, don't use the
    workqueue for log force triggered flushes. Instead, do them directly
    so that the log IO is done directly by the process issuing the log
    force and so doesn't get stuck on IO elevator queue idling
    incorrectly delaying the log IO from the workqueue.
    Signed-off-by: default avatarDave Chinner <dchinner@redhat.com>
    Reviewed-by: default avatarMark Tinguely <tinguely@sgi.com>
    Signed-off-by: default avatarBen Myers <bpm@sgi.com>
    4c2d542f
xfs_super.c 46 KB