crosvm/disk
Takaya Saeki 7781380f01 devices: virtio: block: use fdatasync for FLUSH
Currently, virtio-blk translates a FLUSH request to fsync system call.
However, fsync always updates the metadata of a file, which causes extra
journaling for metadata update. Since virtio-blk cares only the data of
the given block image file, we should avoid updating extra metadata.

After this change, virtio-blk now calls fdatasync for a FLUSH request.
If a write operation wrote to a data block that is already allocated
before, fdatasync can avoid triggering jdb2 journaling on an ext4 file
system.

Note there are structs which fall back to fsync for fdatasync. In
addition, io_uring executor does not implement fdatasync yet.

We observed statistically significant play_store_shown_time improvement
on trogdor-arc-r by -1.614% with this change. Including non
statistically significant data, we observed the following improvements.

|         Name          |  delta  | Count |
|-----------------------|---------|-------|
| trogdor-arc-r (lazor) | -1.614% |  170  |
| brya-arc-t (primus)   | -1.478% |  200  |
| octopus-arc-t (apel)  | -0.887% |  190  |
| kukui-arc-r (kakadu)  | -0.451% |  170  |

BUG=b:281609112
TEST=run a vm with block and confirmed fdatasync is called by strace

Change-Id: Idc94a3ec169e9a5e04394079967f6d79ff4c32db
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/4523029
Commit-Queue: Takaya Saeki <takayas@chromium.org>
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>
2023-05-12 18:15:54 +00:00
..
src devices: virtio: block: use fdatasync for FLUSH 2023-05-12 18:15:54 +00:00
Cargo.toml Cargo.toml: upgrade protobuf 2.x -> 3.x 2023-04-28 19:32:01 +00:00