• Mikulas Patocka's avatar
    powernow-k6: disable cache when changing frequency · cccd0fd7
    Mikulas Patocka authored
    commit e20e1d0a upstream.
    
    I found out that a system with k6-3+ processor is unstable during network
    server load. The system locks up or the network card stops receiving. The
    reason for the instability is the CPU frequency scaling.
    
    During frequency transition the processor is in "EPM Stop Grant" state.
    The documentation says that the processor doesn't respond to inquiry
    requests in this state. Consequently, coherency of processor caches and
    bus master devices is not maintained, causing the system instability.
    
    This patch flushes the cache during frequency transition. It fixes the
    instability.
    
    Other minor changes:
    * u64 invalue changed to unsigned long because the variable is 32-bit
    * move the logic to set the multiplier to a separate function
      powernow_k6_set_cpu_multiplier
    * preserve lower 5 bits of the powernow port instead of 4 (the voltage
      field has 5 bits)
    * mask interrupts when reading the multiplier, so that the port is not
      open during other activity (running other kernel code with the port open
      shouldn't cause any misbehavior, but we should better be safe and keep
      the port closed)
    
    This patch should be backported to all stable kernels. If it doesn't
    apply cleanly, change it, or ask me to change it.
    Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    cccd0fd7
powernow-k6.c 7.04 KB