Messages in this thread | | | Date | Mon, 13 May 2013 11:18:14 -0400 | From | David Oostdyk <> | Subject | Re: high-speed disk I/O is CPU-bound? |
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On 05/12/13 12:53, Rob Landley wrote: > On 05/10/2013 09:04:44 AM, David Oostdyk wrote: >> Hello, >> >> I have a few relatively high-end systems with hardware RAIDs which >> are being used for recording systems, and I'm trying to get a better >> understanding of contiguous write performance. > ... >> The question is, is it possible that high-speed I/O to these hardware >> RAIDs could >> actually be CPU-bound above ~1400MB/sec? > In some setups your processor is calculating CRCs for the data. It's a > fairly cheap operation, but a cheap operation on gigabytes of data can > still saturate your memory bus. > > Rob
At what level would you say this calculation is being applied? Somewhere in the block/filesystem layer, or in the device driver, or at the hardware level? I'm seeing write speeds that are about 1/4 the memory bandwidth of a single thread, which would suggest at least one "additional" pass through the data before it gets DMA'd out.
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