[lkml]   [2000]   [Jul]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    Subjectmap_user_kiobuf problem in 2.4.0-test3

    Here's the scenario:
    2.4.0-test3 SMP build running on a single 800MHz PIII (Dell GX-300)
    After obtaining a mapping to a high memory region (i.e. either
    PCI memory or physical memory reserved by passing mem=XXX to the kernel
    at boot), I am trying to write a raw device with data in the mapped
    This fails, with map_user_kiobuf spitting out "Mapped page missing"
    The raw write works, of course, if the mapping is to a kmalloc'ed

    I have tried the above with 2.2.14 SMP, and it works, so something in
    2.4 is broken.
    On another interesting note: The raw devices I'm writing to are Fibre
    Channel drives controlled by a Qlogic 2200 adapter (in 2.2.14 I'm using
    the Qlogic driver). When writing large sequential blocks to a single
    drive, I reached 8MB/s when the memory was mapped to the high reserved
    region, while CPU utilization was down to about 5%. When the mapping was
    to PCI space, I was able to write at only 4MB/s, and CPU utilization was
    up to 60%! This is very strange, since if the transfer rate was for some
    unknown reason lower in the case of PCI (vs. high physical memory), then
    one would expect the CPU utilization to be even lower, since the adapter
    performs DMA. But instead, the CPU is sweating... So, it appears that
    there's a problem in 2.2.14 as well, when the mapping is to PCI space...
    Additionally, the max transfer rate of 8MB/s seems rather slow - don't
    know why yet...


    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    Please read the FAQ at

     \ /
      Last update: 2005-03-22 13:57    [W:0.031 / U:2.628 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site