• Jens Axboe's avatar
    block: cfq: make the io contect sharing lockless · 4ac845a2
    Jens Axboe authored
    The io context sharing introduced a per-ioc spinlock, that would protect
    the cfq io context lookup. That is a regression from the original, since
    we never needed any locking there because the ioc/cic were process private.
    
    The cic lookup is changed from an rbtree construct to a radix tree, which
    we can then use RCU to make the reader side lockless. That is the performance
    critical path, modifying the radix tree is only done on process creation
    (when that process first does IO, actually) and on process exit (if that
    process has done IO).
    
    As it so happens, radix trees are also much faster for this type of
    lookup where the key is a pointer. It's a very sparse tree.
    Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
    4ac845a2
ll_rw_blk.c 109 KB