block I/O accounting improvements v2

From: Christoph Hellwig
Date: Wed May 27 2020 - 01:26:04 EST

Hi Jens,

they series contains various improvement for block I/O accounting. The
first bunch of patches switch the bio based drivers to better accounting
helpers compared to the current mess. The end contains a fix and various
performanc improvements. Most of this comes from a series Konstantin
sent a few weeks ago, rebased on changes that landed in your tree since
and my change to always use the percpu version of the disk stats.

Changes since v1:
- add an ifdef CONFIG_BLOCK to work around the sad state of our headers
- add reviewed-by tags to all patches