• Shaohua Li's avatar
    md/raid5: sort bios · aaf9f12e
    Shaohua Li authored
    Previous patch (raid5: only dispatch IO from raid5d for harddisk raid)
    defers IO dispatching. The goal is to create better IO pattern. At that
    time, we don't sort the deffered IO and hope the block layer can do IO
    merge and sort. Now the raid5-cache writeback could create large amount
    of bios. And if we enable muti-thread for stripe handling, we can't
    control when to dispatch IO to raid disks. In a lot of time, we are
    dispatching IO which block layer can't do merge effectively.
    
    This patch moves further for the IO dispatching defer. We accumulate
    bios, but we don't dispatch all the bios after a threshold is met. This
    'dispatch partial portion of bios' stragety allows bios coming in a
    large time window are sent to disks together. At the dispatching time,
    there is large chance the block layer can merge the bios. To make this
    more effective, we dispatch IO in ascending order. This increases
    request merge chance and reduces disk seek.
    Signed-off-by: default avatarShaohua Li <shli@fb.com>
    aaf9f12e
raid5.c 236 KB