/ 2006-12-22 10:19:53 -0500
\ Jeff Garzik:
> Lars Ellenberg wrote:
> >md raidX make_request functions strip off the BIO_RW_SYNC flag,
> >this introducing additional latency.
> >below is a suggested patch for the raid1.c .
> >other suggested solutions would be to let the bio_clone do its work,
> >and not reassign thereby stripping off all flags.
> >at most strip off known unwanted flags (the BARRIER flag).
>
> It sounds like a major bug to strip the barrier flag. I quite understand
> that a barrier to a RAID device as a
> whole behaves differently from a barrier to an ATA or SCSI device, but that's
> no excuse to avoid the problem.
sorry for being ambiguous.
this is not about the BARRIER flag.
this is about the BIO_RW_SYNC flag.
> If MD does not pass barriers, it is unilaterally dropping the "data made it
> to the media" guarantee.
MD _does_ pass barriers, unless one of the managed devices reported
EOPNOTSUPP, in which case this is solved differently (reporting EOPNOTSUPP
itself).
the issue at hand is:
because md does special case the barrier bit, it strips off everything
else by re-assigning only the io direction and the barrier bit.
==> I'd like it to also pass at least the sync bit.
I think the better solution would be to _not_ re-assign bi_rw after
bio_clone, and then special case every other bit, but to only strip
off unwanted bits, if at all.
barrier bit was a bad example, because it either is not set,
or gets passed, or is errored as EOPNOTSUPP first thing.
Lars
--
: Lars Ellenberg Tel +43-1-8178292-55 :
: LINBIT Information Technologies GmbH Fax +43-1-8178292-82 :
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