• Coly Li's avatar
    bcache: reduce cache_set devices iteration by devices_max_used · 2831231d
    Coly Li authored
    Member devices of struct cache_set is used to reference all attached
    bcache devices to this cache set. If it is treated as array of pointers,
    size of devices[] is indicated by member nr_uuids of struct cache_set.
    
    nr_uuids is calculated in drivers/md/super.c:bch_cache_set_alloc(),
    	bucket_bytes(c) / sizeof(struct uuid_entry)
    Bucket size is determined by user space tool "make-bcache", by default it
    is 1024 sectors (defined in bcache-tools/make-bcache.c:main()). So default
    nr_uuids value is 4096 from the above calculation.
    
    Every time when bcache code iterates bcache devices of a cache set, all
    the 4096 pointers are checked even only 1 bcache device is attached to the
    cache set, that's a wast of time and unncessary.
    
    This patch adds a member devices_max_used to struct cache_set. Its value
    is 1 + the maximum used index of devices[] in a cache set. When iterating
    all valid bcache devices of a cache set, use c->devices_max_used in
    for-loop may reduce a lot of useless checking.
    
    Personally, my motivation of this patch is not for performance, I use it
    in bcache debugging, which helps me to narrow down the scape to check
    valid bcached devices of a cache set.
    Signed-off-by: default avatarColy Li <colyli@suse.de>
    Reviewed-by: default avatarMichael Lyle <mlyle@lyle.org>
    Reviewed-by: default avatarTang Junhui <tang.junhui@zte.com.cn>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    2831231d
btree.c 56.9 KB