Re: [tbench regression fixes]: digging out smelly deadmen.

[Alan Cox]

> The way to get the best possible dbench numbers in CPU-bound dbench 
> runs, you have to throw away the scheduler completely, and do this 
> instead:
> 
>  - first execute all requests of client 1
>  - then execute all requests of client 2
>  ....
>  - execute all requests of client N

Rubbish. If you do that you'll not get enough I/O in parallel to schedule
the disk well (not that most of our I/O schedulers are doing the job
well, and the vm writeback threads then mess it up and the lack of Arjans
ioprio fixes then totally screw you) </rant>

> the moment the clients are allowed to overlap, the moment their requests 
> are executed more fairly, the dbench numbers drop.

Fairness isn't everything. Dbench is a fairly good tool for studying some
real world workloads. If your fairness hurts throughput that much maybe
your scheduler algorithm is just plain *wrong* as it isn't adapting to
workload at all well.

Alan
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