Just because a device can eat XXX number of tags does definitely _not_
make it a good idea. At least not if you care the slightest bit about
> On the other hand, we can also find a large class of existing devices
> and situations where anything over 4 tags is overload too.
> With some perspective on this, I'd have to say that in the last 25 years
> I've seen more errors on the side of 'too conservative' for limits
> rather than the opposite.
At least for this tagging discussion, I'm of the exact opposite
oppinion. What's the worst that can happen with a tag setting that is
too low? Theoretical loss of disk bandwidth. I say theoretical, because
it's not even given that tags are that much faster then the Linux io
scheduler. More tags might even give you _worse_ throughput, because you
end up leaving the io scheduler with much less to work on (if you have a
253 depth to you device, you have 3 requests left for the queue...).
So I think the 'more tags the better!' belief is very much bogus, at
least for the common case.
-- Jens Axboe
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