• Asias He's avatar
    virtio-blk: Add bio-based IO path for virtio-blk · a98755c5
    Asias He authored
    This patch introduces bio-based IO path for virtio-blk.
    
    Compared to request-based IO path, bio-based IO path uses driver
    provided ->make_request_fn() method to bypasses the IO scheduler. It
    handles the bio to device directly without allocating a request in block
    layer. This reduces the IO path in guest kernel to achieve high IOPS
    and lower latency. The downside is that guest can not use the IO
    scheduler to merge and sort requests. However, this is not a big problem
    if the backend disk in host side uses faster disk device.
    
    When the bio-based IO path is not enabled, virtio-blk still uses the
    original request-based IO path, no performance difference is observed.
    
    Using a slow device e.g. normal SATA disk, the bio-based IO path for
    sequential read and write are slower than req-based IO path due to lack
    of merge in guest kernel. So we make the bio-based path optional.
    
    Performance evaluation:
    -----------------------------
    1) Fio test is performed in a 8 vcpu guest with ramdisk based guest using
    kvm tool.
    
    Short version:
     With bio-based IO path, sequential read/write, random read/write
     IOPS boost         : 28%, 24%, 21%, 16%
     Latency improvement: 32%, 17%, 21%, 16%
    
    Long version:
     With bio-based IO path:
      seq-read  : io=2048.0MB, bw=116996KB/s, iops=233991 , runt= 17925msec
      seq-write : io=2048.0MB, bw=100829KB/s, iops=201658 , runt= 20799msec
      rand-read : io=3095.7MB, bw=112134KB/s, iops=224268 , runt= 28269msec
      rand-write: io=3095.7MB, bw=96198KB/s,  iops=192396 , runt= 32952msec
        clat (usec): min=0 , max=2631.6K, avg=58716.99, stdev=191377.30
        clat (usec): min=0 , max=1753.2K, avg=66423.25, stdev=81774.35
        clat (usec): min=0 , max=2915.5K, avg=61685.70, stdev=120598.39
        clat (usec): min=0 , max=1933.4K, avg=76935.12, stdev=96603.45
      cpu : usr=74.08%, sys=703.84%, ctx=29661403, majf=21354, minf=22460954
      cpu : usr=70.92%, sys=702.81%, ctx=77219828, majf=13980, minf=27713137
      cpu : usr=72.23%, sys=695.37%, ctx=88081059, majf=18475, minf=28177648
      cpu : usr=69.69%, sys=654.13%, ctx=145476035, majf=15867, minf=26176375
     With request-based IO path:
      seq-read  : io=2048.0MB, bw=91074KB/s, iops=182147 , runt= 23027msec
      seq-write : io=2048.0MB, bw=80725KB/s, iops=161449 , runt= 25979msec
      rand-read : io=3095.7MB, bw=92106KB/s, iops=184211 , runt= 34416msec
      rand-write: io=3095.7MB, bw=82815KB/s, iops=165630 , runt= 38277msec
        clat (usec): min=0 , max=1932.4K, avg=77824.17, stdev=170339.49
        clat (usec): min=0 , max=2510.2K, avg=78023.96, stdev=146949.15
        clat (usec): min=0 , max=3037.2K, avg=74746.53, stdev=128498.27
        clat (usec): min=0 , max=1363.4K, avg=89830.75, stdev=114279.68
      cpu : usr=53.28%, sys=724.19%, ctx=37988895, majf=17531, minf=23577622
      cpu : usr=49.03%, sys=633.20%, ctx=205935380, majf=18197, minf=27288959
      cpu : usr=55.78%, sys=722.40%, ctx=101525058, majf=19273, minf=28067082
      cpu : usr=56.55%, sys=690.83%, ctx=228205022, majf=18039, minf=26551985
    
    2) Fio test is performed in a 8 vcpu guest with Fusion-IO based guest using
    kvm tool.
    
    Short version:
     With bio-based IO path, sequential read/write, random read/write
     IOPS boost         : 11%, 11%, 13%, 10%
     Latency improvement: 10%, 10%, 12%, 10%
    Long Version:
     With bio-based IO path:
      read : io=2048.0MB, bw=58920KB/s, iops=117840 , runt= 35593msec
      write: io=2048.0MB, bw=64308KB/s, iops=128616 , runt= 32611msec
      read : io=3095.7MB, bw=59633KB/s, iops=119266 , runt= 53157msec
      write: io=3095.7MB, bw=62993KB/s, iops=125985 , runt= 50322msec
        clat (usec): min=0 , max=1284.3K, avg=128109.01, stdev=71513.29
        clat (usec): min=94 , max=962339 , avg=116832.95, stdev=65836.80
        clat (usec): min=0 , max=1846.6K, avg=128509.99, stdev=89575.07
        clat (usec): min=0 , max=2256.4K, avg=121361.84, stdev=82747.25
      cpu : usr=56.79%, sys=421.70%, ctx=147335118, majf=21080, minf=19852517
      cpu : usr=61.81%, sys=455.53%, ctx=143269950, majf=16027, minf=24800604
      cpu : usr=63.10%, sys=455.38%, ctx=178373538, majf=16958, minf=24822612
      cpu : usr=62.04%, sys=453.58%, ctx=226902362, majf=16089, minf=23278105
     With request-based IO path:
      read : io=2048.0MB, bw=52896KB/s, iops=105791 , runt= 39647msec
      write: io=2048.0MB, bw=57856KB/s, iops=115711 , runt= 36248msec
      read : io=3095.7MB, bw=52387KB/s, iops=104773 , runt= 60510msec
      write: io=3095.7MB, bw=57310KB/s, iops=114619 , runt= 55312msec
        clat (usec): min=0 , max=1532.6K, avg=142085.62, stdev=109196.84
        clat (usec): min=0 , max=1487.4K, avg=129110.71, stdev=114973.64
        clat (usec): min=0 , max=1388.6K, avg=145049.22, stdev=107232.55
        clat (usec): min=0 , max=1465.9K, avg=133585.67, stdev=110322.95
      cpu : usr=44.08%, sys=590.71%, ctx=451812322, majf=14841, minf=17648641
      cpu : usr=48.73%, sys=610.78%, ctx=418953997, majf=22164, minf=26850689
      cpu : usr=45.58%, sys=581.16%, ctx=714079216, majf=21497, minf=22558223
      cpu : usr=48.40%, sys=599.65%, ctx=656089423, majf=16393, minf=23824409
    
    3) Fio test is performed in a 8 vcpu guest with normal SATA based guest
    using kvm tool.
    
    Short version:
     With bio-based IO path, sequential read/write, random read/write
     IOPS boost         : -10%, -10%, 4.4%, 0.5%
     Latency improvement: -12%, -15%, 2.5%, 0.8%
    Long Version:
     With bio-based IO path:
      read : io=124812KB, bw=36537KB/s, iops=9060 , runt=  3416msec
      write: io=169180KB, bw=24406KB/s, iops=6065 , runt=  6932msec
      read : io=256200KB, bw=2089.3KB/s, iops=520 , runt=122630msec
      write: io=257988KB, bw=1545.7KB/s, iops=384 , runt=166910msec
        clat (msec): min=1 , max=1527 , avg=28.06, stdev=89.54
        clat (msec): min=2 , max=344 , avg=41.12, stdev=38.70
        clat (msec): min=8 , max=1984 , avg=490.63, stdev=207.28
        clat (msec): min=33 , max=4131 , avg=659.19, stdev=304.71
      cpu          : usr=4.85%, sys=17.15%, ctx=31593, majf=0, minf=7
      cpu          : usr=3.04%, sys=11.45%, ctx=39377, majf=0, minf=0
      cpu          : usr=0.47%, sys=1.59%, ctx=262986, majf=0, minf=16
      cpu          : usr=0.47%, sys=1.46%, ctx=337410, majf=0, minf=0
    
     With request-based IO path:
      read : io=150120KB, bw=40420KB/s, iops=10037 , runt=  3714msec
      write: io=194932KB, bw=27029KB/s, iops=6722 , runt=  7212msec
      read : io=257136KB, bw=2001.1KB/s, iops=498 , runt=128443msec
      write: io=258276KB, bw=1537.2KB/s, iops=382 , runt=168028msec
        clat (msec): min=1 , max=1542 , avg=24.84, stdev=32.45
        clat (msec): min=3 , max=628 , avg=35.62, stdev=39.71
        clat (msec): min=8 , max=2540 , avg=503.28, stdev=236.97
        clat (msec): min=41 , max=4398 , avg=653.88, stdev=302.61
      cpu          : usr=3.91%, sys=15.75%, ctx=26968, majf=0, minf=23
      cpu          : usr=2.50%, sys=10.56%, ctx=19090, majf=0, minf=0
      cpu          : usr=0.16%, sys=0.43%, ctx=20159, majf=0, minf=16
      cpu          : usr=0.18%, sys=0.53%, ctx=81364, majf=0, minf=0
    
    How to use:
    -----------------------------
    Add 'virtio_blk.use_bio=1' to kernel cmdline or 'modprobe virtio_blk
    use_bio=1' to enable ->make_request_fn() based I/O path.
    
    Cc: Rusty Russell <rusty@rustcorp.com.au>
    Cc: Jens Axboe <axboe@kernel.dk>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Shaohua Li <shli@kernel.org>
    Cc: "Michael S. Tsirkin" <mst@redhat.com>
    Cc: kvm@vger.kernel.org
    Cc: linux-kernel@vger.kernel.org
    Cc: virtualization@lists.linux-foundation.org
    Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
    Signed-off-by: default avatarMinchan Kim <minchan.kim@gmail.com>
    Signed-off-by: default avatarAsias He <asias@redhat.com>
    Acked-by: default avatarRusty Russell <rusty@rustcorp.com.au>
    Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
    a98755c5
virtio_blk.c 22.2 KB