On 12/10/18 9:35 AM, Dennis Zhou wrote: > The blk-iolatency controller measures the time from rq_qos_throttle() to > rq_qos_done_bio() and attributes this time to the first bio that needs > to create the request. This means if a bio is plug-mergeable or > bio-mergeable, it gets to bypass the blk-iolatency controller. > > The recent series, to tag all bios w/ blkgs in [1] changed the timing > incorrectly as well. First, the iolatency controller was tagging bios > and using that information if it should process it in rq_qos_done_bio(). > However, now that all bios are tagged, this caused the atomic_t for the > struct rq_wait inflight count to underflow resulting in a stall. Second, > now the timing was using the duration a bio from generic_make_request() > rather than the timing mentioned above. > > This patch fixes the errors by accounting time separately in a bio > adding the field bi_start. If this field is set, the bio should be > processed by blk-iolatency in rq_qos_done_bio(). > > [1] https://lore.kernel.org/lkml/20181205171039.73066-1-dennis@xxxxxxxxxx/ Looks reasonable to me, but it needs a Fixes tag as well. -- Jens Axboe
