On 10/21/23 00:32, Yu Kuai wrote:
Sorry for such huge delay, I was struggled on implementing a smoothly algorithm to borrow tags and return borrowed tags, and later I put this on ice and focus on other stuff. I had an idea to implement a state machine, however, the amount of code was aggressive and I gave up. And later, I implemented a simple version, and I tested it in your case, 32 tags and 2 shared node, result looks good(see below), however, I'm not confident this can work well general. Anyway, I'll send a new RFC verion for this, and please let me know if you still think this approch is unacceptable. Thanks, Kuai Test script: [global] ioengine=libaio iodepth=2 bs=4k direct=1 rw=randrw group_reporting [sda] numjobs=32 filename=/dev/sda [sdb] numjobs=1 filename=/dev/sdb Test result, by monitor new debugfs entry shared_tag_info: time active available sda sdb sda sdb 0 0 0 32 32 1 16 2 16 16 -> start fair sharing 2 19 2 20 16 3 24 2 24 16 4 26 2 28 16 -> borrow 32/8=4 tags each round 5 28 2 28 16 -> save at lease 4 tags for sdb
Hi Yu, Thank you for having shared these results. What is the unit of the numbers in the time column? In the above I see that more tags are assigned to sda than to sdb although I/O is being submitted to both LUNs. I think the current algoritm defines fairness as dividing tags in a fair way across active LUNs. Do the above results show that tags are divided per active job instead of per active LUN? If so, I'm not sure that everyone will agree that this is a fair way to distribute tags ... Thanks, Bart.
