[Pvfs2-developers] Coalesce patch

[Julian Martin Kunkel]

Hi,
Thanks, hope the patch works alright...
>  I'm not convinced this is the best value for the default case.  
> If the server can handle operations fast enough that the queue  
> remains at 1, coalescing doesn't seem necessary, and it will give  
> widely varied timings for some of the operations of some clients.
I think in general this is a good value, but change it if you like.

If the disk is fast enough that the queue remains at 1 the loss is small 
(depending on the processing time), however you are right it slows the first 
one down. 

Argument for setting it to 1:
We want to coalesce as much ops as possible, assume each sync costs 5 ms (disk 
access time) while a non-blocking modification might take 0.1ms. 
If somebody has 2 ops in the queue and the low watermark is 2 the first 
finishes on 5.1 ms, while the second finishes on 10.2 ms.
In case the watermark is 1 the first and the second one finishs at 5.2 ms.
Even if you assume that the op might be blocking I would say for the majority 
of people setting it to 1 reduce the overall op time.


julian