Re: Quick bcache benchmark

[Kent Overstreet <kent.overstreet-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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

> 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...