Make foreground and background I/O priority different

Assign a higher I/O priority to foreground I/O compared to background
I/O to improve responsiveness of the foreground app.

The command below shows that this CL has the intended effect on a device
with kernel 5.10:

    $ adb shell 'cd /dev/blkio && grep -aH . blkio.prio.class background/blkio.prio.class'
    blkio.prio.class:none-to-rt
    background/blkio.prio.class:restrict-to-be

From a device with an Android 6.1 kernel:

    $ grep -aH . blkio.prio.class background/blkio.prio.class'
    blkio.prio.class:promote-to-rt
    background/blkio.prio.class:restrict-to-be

Bug: 347109476
Change-Id: I6f1ea6a89a8dfaa223e8d2a82917b4de2d7bf1cf
Signed-off-by: Bart Van Assche <bvanassche@google.com>
1 file changed