Re: [PATCH 4/8] Btrfs: stop using btrfs_schedule_bio()
From: Josef Bacik <josef@toxicpanda.com>
Date: 2019-06-14 13:45:07
Also in:
linux-btrfs, lkml
On Thu, Jun 13, 2019 at 05:33:46PM -0700, Tejun Heo wrote:
From: Chris Mason <clm@fb.com> btrfs_schedule_bio() hands IO off to a helper thread to do the actual submit_bio() call. This has been used to make sure async crc and compression helpers don't get stuck on IO submission. To maintain good performance, over time the IO submission threads duplicated some IO scheduler characteristics such as high and low priority IOs and they also made some ugly assumptions about request allocation batch sizes. All of this cost at least one extra context switch during IO submission, and doesn't fit well with the modern blkmq IO stack. So, this commit stops using btrfs_schedule_bio(). We may need to adjust the number of async helper threads for crcs and compression, but long term it's a better path. Signed-off-by: Chris Mason <clm@fb.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com> Thanks, Josef