On Mar 4, 2006, at 2:10 PM, Jeff Garzik wrote:
Steve Byan wrote:
Data integrity -and- performance. Performance increases for all
the standard reasons that an asynchronous pipeline increases
performance over a synchronous one.
The write cache means that requests on the device can be
processed asynchronously, but without NCQ there is still a
synchronous bottleneck: the device<->controller pipe.
True, but I think that is fairly small compared to no-write-cache-
and- no-queuing case. Write-caching is the major win; optimizing
the data transfer is only a second-order effect.
Measurements on NCQ in the field show a distinct performance
improvement... 30% has been measured on Linux. Nothing to sneeze at.
Wow! 30% is amazing. I'd be interested in knowing how the costs break
down; are these measurements published anywhere?
Regards,
-Steve
--
Steve Byan <smb@xxxxxxxxxxx>
Software Architect
Egenera, Inc.
165 Forest Street
Marlboro, MA 01752
(508) 858-3125
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