On Jul 12, 2006, at 3:44 PM, Julian Martin Kunkel wrote:
Hi,
Thanks, hope the patch works alright...
Can you change the immediate completion flag and send another?
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.
No if there are 2 ops in the queue and the low watermark is set to 2
than they get coalesced. The case you're probably looking for is if
the low watermark is set to two, and the queue never gets higher than
1, but the second operation is added to the queue while the first is
being serviced. Its true that the 2 consecutive syncs will take ~ 10
ms total instead of something like ~ 7 ms, but at least the first
operation isn't taking 2 ms longer. Remember that this specific
scenario means that the client is only sending requests at a rate of
~ 5 ms, so individual syncs don't really cost anything.
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
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