On Thu, 2 Mar 2006, Douglas Gilbert wrote:
>
> As more information has come to light, the worst case
> "big transfer" of a single SCSI command through sg (and
> st I suspect) is 512 KB **. With full coalescing that figure
> goes up to 4 MB **. I am also aware that some users
> increase SG_SCATTER_SZ in the sg driver to get larger
> "big transfer"s than sg's current limit of (8MB - 32KB) **.
> That facility has now gone (i.e. upping SG_SCATTER_SZ will
> have no effect) with no replacement mechanism.
>
> So I'll add my vote to "revert this change before lk 2.6.16"
> with a view to applying it after some solution to the "big
> transfer" problem is found.
Considering that the old code was apparently known-broken due to not
honoring the use_clustering flag, I would say that the more likely thing
is that very few people use sg in the first place, and we should wait and
see what the reaction is to actually fixing a real bug.
Doing more than page-sized transfers can be hard/impossible in virtualized
environments, for example.
In contrast, upping the limits should be fairly easy, I assume. Same goes
for if some driver disables clustering even though it shouldn't. No?
Linus
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