[stgt] [PATCH 1/3] NOT_LAST bit in cmd state, enables batch submission

[Alexander Nezhinsky]

On 11/08/2011 03:46 AM, FUJITA Tomonori wrote:

> 
> Batching commands sounds good. I've not read the patches though. Have
> you measured that how this could improve the performance?


Yes, i have measured the performance. Improvements depend on the workload
type, the storage device characteristics, and the type of the servers. 
The main improvement is for IOPS. 
I saw (over iser/ib to FusionIo SSD) improvement of 5-20% for write 
and 3-15% for read IOPS (1kb) for various loads/setups. 
Typical values 55Kiops -> 62Kiops, 90kiops -> 100kiops

iser can enjoy batching because it repeatedly polls the Completion Queue and
may found multiple cmds in one polling sweep. It stores them on a list and
instantly processes it and submits the commands. Here it treats the commands
which already present on the list as a batch, so the processing is never 
actually deferred in order to get some more. Only if some commands are 
"already here" anyway, are they marked as a batch.

Do you see how other transports, notably iscsi/tcp can employ a similar scheme?
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