Re: [RFC][PATCH] sard changes for 2.5.34

[Andrew Morton <akpm@digeo.com>]

Rick Lindsley wrote:
> 
> Here's a patch to put sard changes similar to those in 2.4 into 2.5.  I
> say "similar" because the I/O subsystem has changed sufficiently in 2.5
> that making them exactly the same might be more effort that it's
> worth.  Still, we do record per-partition reads/writes/sectors, and
> per-disk stats on the same plus queue time and number of I/O merges.
> Once applied, "cat /proc/diskstats" outputs this information.

It would be very nice to get better disk accounting into the kernel.

> Because in 2.5.34, gendisk->part[0] no longer is an hd_struct that
> refers to the whole disk, there wasn't a convenient place to record
> this information.  I gratuitously added an hd_struct to gendisk to have
> a place to store the information, below, but that's distasteful and
> ugly. I'd like to move it to a different place.
> 
> Also, with this patch, we are collecting stats twice, once for these
> stats and once for /proc/stat (kstat).  That's stupid and I'd like to
> get the stats only once and use them, perhaps, in two places.

kstat should be a lighter-weight per-cpu thing.  But the current
disk accounting in there would make it 12 kilobytes per CPU.

My vote: remove the disk accounting from kernel_stat and use this.
 
> What follows works, but needs refinements.  Comments welcome.

What are those refinements?

What userspace tools are available for interpreting this information?