• Stefani Seibold's avatar
    mtd: fix a huge latency problem in the MTD CFI and LPDDR flash drivers. · c4e77376
    Stefani Seibold authored
    The use of a memcpy() during a spinlock operation will cause very long
    thread context switch delays if the flash chip bandwidth is low and the
    data to be copied large, because a spinlock will disable preemption.
    
    For example: A flash with 6,5 MB/s bandwidth will cause under ubifs,
    which request sometimes 128 KiB (the flash erase size), a preemption delay of
    20 milliseconds. High priority threads will not be served during this
    time, regardless whether this threads access the flash or not. This behavior
    breaks real time.
    
    The patch changes all the use of spin_lock operations for xxxx->mutex
    into mutex operations, which is exact what the name says and means.
    
    I have checked the code of the drivers and there is no use of atomic
    pathes like interrupt or timers. The mtdoops facility will also not be used
    by this drivers. So it is dave to replace the spin_lock against mutex.
    
    There is no performance regression since the mutex is normally not
    acquired.
    
    Changelog:
     06.03.2010 First release
     26.03.2010 Fix mutex[1] issue and tested it for compile failure
    Signed-off-by: default avatarStefani Seibold <stefani@seibold.net>
    Signed-off-by: default avatarArtem Bityutskiy <Artem.Bityutskiy@nokia.com>
    Signed-off-by: default avatarDavid Woodhouse <David.Woodhouse@intel.com>
    c4e77376
cfi_cmdset_0020.c 37.6 KB