Re: [PATCH 00/33] Adaptive read-ahead V12

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If the developers of that program want to squeeze the last 5% out of it
then sure, I'd expect them to use such OS-provided I/O scheduling
facilities.  Database developers do that sort of thing all the time.

We have an application which knows what it's doing sending IO requests to
the kernel which must then try to reverse engineer what the application is
doing via this rather inappropriate communication channel.

Is that dumb, or what?

Given that the application already knows what it's doing, it's in a much
better position to issue the anticipatory IO requests than is the kernel.

if a program is trying to squeeze every last bit of performance out of a system then you are right, it should run on the bare hardware. however in reality many people are willing to sacrafice a little performance for maintainability, and portability.

if Adaptive read-ahead was only useful for Postgres (and had a negative effect on everything else, even if it's just the added complication in the kernel) then I would agree that it should be in Postgres, not in the kernel. but I don't believe that this is the case, this patch series helps in a large number of workloads (including 'cp' according to some other posters), postgres was just used as the example in this subthread.

gnome startup has some serious read-ahead issues from what I've heard, should it include an I/O scheduler as well (after all it knows what it's going to be doing, why should the kernel have to reverse-enginer it)

David Lang

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