From: David Oostdyk <daveo@ll.mit.edu>
To: Rob Landley <rob@landley.net>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: high-speed disk I/O is CPU-bound?
Date: Mon, 13 May 2013 11:18:14 -0400 [thread overview]
Message-ID: <51910436.6070509@ll.mit.edu> (raw)
In-Reply-To: <1368377617.18069.228@driftwood>
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.
next prev parent reply other threads:[~2013-05-13 15:18 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-10 14:04 high-speed disk I/O is CPU-bound? David Oostdyk
2013-05-11 0:19 ` Eric Wong
2013-05-13 14:58 ` David Oostdyk
2013-05-12 16:53 ` Rob Landley
2013-05-13 15:18 ` David Oostdyk [this message]
2013-05-16 0:59 ` Dave Chinner
2013-05-16 0:59 ` Dave Chinner
2013-05-16 11:36 ` Stan Hoeppner
2013-05-16 11:36 ` Stan Hoeppner
2013-05-16 15:35 ` David Oostdyk
2013-05-16 15:35 ` David Oostdyk
2013-05-16 22:56 ` Dave Chinner
2013-05-16 22:56 ` Dave Chinner
2013-05-17 11:56 ` Stan Hoeppner
2013-05-17 11:56 ` Stan Hoeppner
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