Hello,
Kai Makisara wrote:
* st uses three retry limits - MAX_RETRIES, MAX_WRITE_RETRIES and
MAX_READY_RETRIES, which are all zero. This patch only converts
MAX_RETRIES to sdev->retries. Defining WRITE and READY retries in
terms of sdev->retries would make more sense.
I am neither acking nor naking this now. The patch does not change st
behavior but moves part of the retry strategy out of the driver. (Which is
also good because it makes one of the retry limits user changeable.)
Combining all retry counts is something that may not be a good thing.
Below is justification why st has three different retry limits.
For some devices one number of retries is not perfect for all functions.
The firmware of tape devices usually retries quite thoroughly before
returning error. This is why the default zero applies to most cases.
MAX_WRITE_RETRIES is separate from MAX_RETRIES because a plausible
strategy might be (maybe not any more) to allow no retries for write but
allow retries for reading and repositioning. The writes should fail
directly so that the minimum number of marginal errors will be written.
The reads can be retried so that even marginal data can be recovered.
(Note that this may lead to tape positioning errors and may not be a
good strategy in all cases.)
MAX_READY_RETRIES is used for commands that don't move the tape. This is a
situation where retrying is probably harmless.
I see. Then, how about adding and initializing STp->write_retries and
STp->ready_retries according to SDp->retries (some reasonable default
value, say write_retries is always zero while ready_retries is round up
of retries * 1.1) and export both through sysfs? That will give lower
level primitive control as other ULDs do and also allow users to
configure each timeout separately if necessary.
Thanks.
--
tejun
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