Re: [PATCH] btrfs: sysfs: export dev stats in devinfo directory

[David Sterba <dsterba@suse.cz>]

On Sat, Jun 05, 2021 at 06:38:16AM +0800, Anand Jain wrote:
> On 04/06/2021 22:21, David Sterba wrote:
> > On Fri, Jun 04, 2021 at 09:41:09PM +0800, Anand Jain wrote:
> >> On 4/6/21 9:20 pm, David Sterba wrote:
> >>> The device stats can be read by ioctl, wrapped by command 'btrfs device
> >>> stats'. Provide another source where to read the information in
> >>> /sys/fs/btrfs/FSID/devinfo/DEVID/stats .
> >>
> >>    The planned stat here is errors stat.
> >>    So why not rename this to error_stats?
> > 
> > I think it's commonly called device stats, dev stats, so when it's in
> > 'devinfo' it's like it's the 'stats' for the device.
> 
> 
> > We don't have other
> > stats, like regarding io but in that case it would make sense to
> > distnguish the names.
> 
> My read_policy work (which I suppose is next on your list for review) 

Yeah, it's among the next things to merge once the current features
stabilize enough.

> made sense that publishing the io-stat information locally from btrfs is 
> a good idea. So that it provides clarity if the IO is skewed to a device 
> or balanced. Which is even more essential in the case of mixed device 
> types. For now IMHO,  /sys/fs/btrfs/FSID/devinfo/DEVID/error_stats
> is harmless.

Agreed, I thought about the same, gathering some regular io stats, so
the error_stats makes sense. There's still one open question whether to
do it all in one file or in a subdirectory error_stats/ . The sysfs way
is one value per file but for the stats I'm more inclined to follow what
/proc/ stats do. It's more convenient to monitor stats in one file read
than having to do 'cat error_stats/*' or with filenames as 'grep ^
error_stats/*'.