• Jens Axboe's avatar
    [PATCH] pipe: enable atomic copying of pipe data to/from user space · f6762b7a
    Jens Axboe authored
    The pipe ->map() method uses kmap() to virtually map the pages, which
    is both slow and has known scalability issues on SMP. This patch enables
    atomic copying of pipe pages, by pre-faulting data and using kmap_atomic()
    instead.
    
    lmbench bw_pipe and lat_pipe measurements agree this is a Good Thing. Here
    are results from that on a UP machine with highmem (1.5GiB of RAM), running
    first a UP kernel, SMP kernel, and SMP kernel patched.
    
    Vanilla-UP:
    Pipe bandwidth: 1622.28 MB/sec
    Pipe bandwidth: 1610.59 MB/sec
    Pipe bandwidth: 1608.30 MB/sec
    Pipe latency: 7.3275 microseconds
    Pipe latency: 7.2995 microseconds
    Pipe latency: 7.3097 microseconds
    
    Vanilla-SMP:
    Pipe bandwidth: 1382.19 MB/sec
    Pipe bandwidth: 1317.27 MB/sec
    Pipe bandwidth: 1355.61 MB/sec
    Pipe latency: 9.6402 microseconds
    Pipe latency: 9.6696 microseconds
    Pipe latency: 9.6153 microseconds
    
    Patched-SMP:
    Pipe bandwidth: 1578.70 MB/sec
    Pipe bandwidth: 1579.95 MB/sec
    Pipe bandwidth: 1578.63 MB/sec
    Pipe latency: 9.1654 microseconds
    Pipe latency: 9.2266 microseconds
    Pipe latency: 9.1527 microseconds
    Signed-off-by: default avatarJens Axboe <axboe@suse.de>
    f6762b7a
pipe.c 21.3 KB