I suspect it may just be that "queue_nr_requests"/"batch_count" is
different in -ac: what happens if you tweak them to the same values?
(See drivers/block/ll_rw_block.c)
I think -ac made the queues a bit deeper the regular kernel does 128
requests and a batch-count of 16, I _think_ -ac does something like "2
requests per megabyte" and batch_count=32, so if you have 512MB you should
try with
queue_nr_requests = 1024
batch_count = 32
Does that help?
Linus
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