On Fri, Apr 04, 2014 at 12:10:53PM -0700, Kent Overstreet wrote: > How much data is being bypassed? > > On Fri, Apr 4, 2014 at 10:06 AM, Andrew Martin <amartin@xxxxxxxxxxx> wrote: > > > > Am I doing something wrong when running fio? Andrew, There's not enough information to be able to say if something is going wrong at this stage as I don't know: a) The speed of the backing device (also the block device name (e.g. sda/md0 helps later)) with a given IO pattern b) The speed of the front device (block name also helps later) with a given IO pattern c) What bcache settings you have set d) What type of IO was done to the bcache device and at which points (e.g. was writeback happening at that point?) e) What statistics bcache is reporting Initially while you're getting used to this I'd stick to just running one block size (4k). So something like: export RT=30; export SEED=21; export SIZE="5G"; export DEV="bcache0"; BS="4k" Ensure you have read and implemented the appropriate pieces mentioned in the TROUBLESHOOTING PERFORMANCE section of https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/bcache.txt#n130 otherwise results can be unexpected when benchmarking... Something like the following would be easier to follow: Set the cache_mode to none. Run (and record) grep -r . /sys/block/bcache0/bcache/ Clear the bcache total stats (see clear_stats) View and record the bcache backing device total stats then run fio benchmark-rand.fio View and record the bcache backing device total stats Set the cache_mode to writeback. Run (and record) grep -r . /sys/block/bcache0/bcache/ Clear the bcache total stats then run View and record the bcache backing device total stats then run fio benchmark-rand.fio View and record the bcache backing device total stats If everything is working (and the front device is faster for random writes) I'd expect the with writeback fio job to be noticibly faster than none fio job (how much faster is setup dependent). Only if my expectation was correct would I repeat the above with the benchmark-seq.fio job... -- Sitsofe | http://sucs.org/~sits/ -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
