Re: Quick bcache benchmark

That keeps the 'bypassed' value from increasing, but it doesn't change
write performance.

BEFORE:
[root@sansrv2-10 stats_day]# cat *
27.6M
83
3500
0
166
24380
40660
0

...benchmarking...

AFTER:

[root@sansrv2-10 stats_day]#  for i in `ls`; do echo -n "$i "; cat $i;

done 2>/dev/null

bypassed 27.6M
cache_bypass_hits 83
cache_bypass_misses 3500
cache_hit_ratio 0
cache_hits 410
cache_miss_collisions 48879
cache_misses 80545
cache_readaheads 0

/sys/fs/bcache/60da061c-d646-4ebe-931a-d8580add411d

average_key_size 0
block_size 2.0k
btree_cache_size 3.2M
bucket_size 1.0M
cache_available_percent 100
clear_stats congested 0
congested_threshold_us 0
dirty_data 0
io_error_halflife 0
io_error_limit 8
root_usage_percent 0
synchronous 1
tree_depth 1


On Fri, Dec 9, 2011 at 11:33 PM, Kent Overstreet
[off-list ref] wrote:

On Fri, Dec 09, 2011 at 10:09:55AM -0700, Marcus Sorensen wrote:

quoted

Here's some more info. I'm running kernel 3.1.4. When I do random
writes, the 'bypassed' number increases in stats. Now I'm random
writing direct to /dev/bcache0 and get the same result.

Weird. From what you're describing it sounds like throttling is screwed
up (and it was recently), but I can't reproduce it now.

Can you try echoing 0 to congested_threshold_us in the cache set dir,
and seeing if that fixes it?

quoted

There also seems to be some work needed with clean-up, since I'm
unfamiliar with how bcache works I attempted to make-bcache twice,
thinking I'd start over. That worked, but because my cache device was
already registered I was unable to re-register my newly formatted
cache dev, got "kobject_add_internal failed for bcache with -EEXIST,
don't try to register things with the same name in the same
directory." I was still able to use my cache device via the old uuid,
but this will probably cause problems on reboot. Perhaps an unregister
file in /sys/fs/bcache would help, I also tried rmmod'ing bcache to
see if I could clear /sys/fs/bcache, but no luck. make-bcache should
perhaps check for an existing superblock, ask for confirmation, and
give some sort instruction on how to unregister, or do it for you if
you reformat.

Yeah, I think for some reason bcache isn't opening the devices
exclusively on 3.1. I'll have a look...