Re: Default cache_hot_time value back to 10ms

[Andrew Morton]

Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote:
>
>  Andrew Morton wrote:
>  > "Chen, Kenneth W" <kenneth.w.chen@xxxxxxxxx> wrote:
>  > 
>  >>This value was default to 10ms before domain scheduler, why does domain
>  >> scheduler need to change it to 2.5ms? And on what bases does that decision
>  >> take place?  We are proposing change that number back to 10ms.
>  > 
>  > 
>  > It sounds like this needs to be runtime tunable?
>  > 
> 
>  I'd say it is probably too low level to be a useful tunable (although
>  for testing I guess so... but then you could have *lots* of parameters
>  tunable).

This tunable caused an 11% performance difference in (I assume) TPCx. 
That's a big deal, and people will want to diddle it.

If one number works optimally for all machines and workloads then fine.

But yes, avoiding a tunable would be nice, but we need a tunable to work
out whether we can avoid making it tunable ;)

Not that I'm soliciting patches or anything.  I'll duck this one for now.
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