• Ming Lei's avatar
    blk-mq: complete req in softirq context in case of single queue · 36e76539
    Ming Lei authored
    Lot of controllers may have only one irq vector for completing IO
    request. And usually affinity of the only irq vector is all possible
    CPUs, however, on most of ARCH, there may be only one specific CPU
    for handling this interrupt.
    
    So if all IOs are completed in hardirq context, it is inevitable to
    degrade IO performance because of increased irq latency.
    
    This patch tries to address this issue by allowing to complete request
    in softirq context, like the legacy IO path.
    
    IOPS is observed as ~13%+ in the following randread test on raid0 over
    virtio-scsi.
    
    mdadm --create --verbose /dev/md0 --level=0 --chunk=1024 --raid-devices=8 /dev/sdb /dev/sdc /dev/sdd /dev/sde /dev/sdf /dev/sdg /dev/sdh /dev/sdi
    
    fio --time_based --name=benchmark --runtime=30 --filename=/dev/md0 --nrfiles=1 --ioengine=libaio --iodepth=32 --direct=1 --invalidate=1 --verify=0 --verify_fatal=0 --numjobs=32 --rw=randread --blocksize=4k
    
    Cc: Dongli Zhang <dongli.zhang@oracle.com>
    Cc: Zach Marano <zmarano@google.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Bart Van Assche <bvanassche@acm.org>
    Cc: Jianchao Wang <jianchao.w.wang@oracle.com>
    Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    36e76539
blk-softirq.c 4.46 KB