Nick Piggin wrote:
> Actually, I would still like to be able to deprecate deadline for
> AS, because AS has a tunable that you can switch to turn off read
> anticipation and revert to deadline behaviour (or very close to).
You mean antic_expire? I tried it, and it does have an enormous effect on
performance. Smaller values do mimic deadline behavior in a way, as
deadline has some strange behaviour on sync, so it's closer to noop, which
is good for single user/proc access, while larger values are good for multi
user/proc access. But I always have to set it to 0, or else it starves sync
with others reading.
I wonder if these tunables couldn't be autotuned by some form of
history-based access pattern detection?
> It would have been nice if CFQ were then a layer on top of AS that
> implemented priorities (or vice versa). And then AS could be
> deprecated and we'd be back to 1 primary scheduler.
>
> Well CFQ seems to be going in the right direction with that, however
> some large users still find AS faster for some reason...
AS is faster no-contest. CFQ has some deep block-io/queue problem that slows
it down up to 25%. It's related to max_sectors_kb and read_ahead_kb , and I
mentioned this to Jens before, and AS show this problem sometimes too, but
with CFQ it's much more prevalent.
Thanks!
--
Al
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