On 12/12/23 13:52, Damien Le Moal wrote:
Trying to solve this issue in mq-deadline would require keeping track of the io
priority used for a write request that is issued to a zone and use that same
priority for all following write requests for the same zone until there are no
writes pending for that zone. Otherwise, you will get the priority inversion
causing the reordering.
But I think that doing all this without also causing priority inversion for the
user, i.e. a high priority write request ends up waiting for a low priority one,
will be challenging, to say the least.
Hi Damien,
How about the following algorithm?
- If a zoned write refers to the start of a zone or no other writes for
the same zone occur in the RB-tree, use the I/O priority of the zoned
write.
- If another write for the same zone occurs in the RB-tree, use the I/O
priority from that other write.
While this algorithm does not guarantee that all zoned writes for a
single zone have the same I/O priority, it guarantees that the
mq-deadline I/O scheduler won't submit zoned writes in the wrong order
because of their I/O priority.
Thanks,
Bart.
