Use ftrace to trace block event, and found the blow when bad read
performance[1] is observed:
mmcqd/0-57 [000] 8827.689789: block_rq_issue: 179,0 W 0 () 5653017
+ 8 [mmcqd/0]
mmcqd/0-57 [000] 8828.408600: block_rq_complete: 179,0 W ()
5653017 + 8 [0]
Seems the bad read performance is caused by slow write operation, as traced by
above:
over 700ms is spent to write 8 sectors.
The slow write can be often happened, but not each time.
[1], use dd to test read performance on mmc card:
#dd if=/dev/mmcblk0p1 iflag=direct of=/dev/null bs=65536 count=40
40+0 records in
40+0 records out
2621440 bytes (2.6 MB) copied, 10.0263 s, 261 kB/s
[2], block event trace log, see attachment.
** Attachment added: "mmc-tr-dd-rd-261K.trace"
https://bugs.launchpad.net/ubuntu/+source/linux-ti-omap4/+bug/784421/+attachment/2176909/+files/mmc-tr-dd-rd-261K.trace
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https://bugs.launchpad.net/bugs/784421
Title:
natty slow boot on pandaboard(rev A1)
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