Ric Wheeler wrote:
May 17 03:30:54 centera kernel: [start_ordered ]: BIO d08998c0 3357330 4096
May 17 03:30:54 centera kernel: [start_ordered ]: ordered=1 in_flight=0
May 17 03:30:54 centera kernel: [blk_do_ordered ]: start_ordered ed3553c0->dfe2bd28
May 17 03:30:54 centera kernel: [elv_next_request ]: dfe2bd28 (bar)
May 17 03:30:54 centera kernel: [ordered_bio_endio ]: q->orderr=0 error=0
May 17 03:30:54 centera kernel: [flush_dry_bio_endio ]: BIO f18ffa00 3357330 4096
May 17 03:30:54 centera kernel: [blk_ordered_complete_seq]: ordseq=17 seq=08 orderr=0 error=0
May 17 03:30:54 centera kernel: [blk_ordered_complete_seq]: sequence complete
May 17 03:30:54 centera kernel: [ordered_bio_endio ]: q->orderr=0 error=0
May 17 03:30:54 centera kernel: [flush_dry_bio_endio ]: BIO f18ff300 3357330 4096
May 17 03:30:54 centera kernel: [blk_ordered_complete_seq]: ordseq=17 seq=08 orderr=0 error=0
May 17 03:30:54 centera kernel: [blk_ordered_complete_seq]: sequence complete
[--snip--]
Combined with your boot log, everything seems as expected. Write cache
is disabled, so the chosen ordered mode is 0x1 - DRAIN only. In the log
you've posted, there are no pending IOs on barrier issue, so the barrier
is executed directly and then the sequence is complete. If there were
other requests pending, all that happens would be waiting for them to
finish before issuing the barrier.
If you turned on write cache after the machine booted, what method did
you use to turn on write cache? If you issued the command directly
using sg to an active device (usage count >= 1), SCSI doesn't snoop such
commands and thus it won't adjust ordered mode automatically. However,
sd forces disk revalidation (and thus ordered reconfiguration) if you
change cache mode via /sys/class/scsi_disk/X\:0\:0\:0/cache_type.
--
tejun
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