Re: IDE throughput in 2.6 - it's good!

Timothy Miller
2004-04-27T20:40:05Z

Ken Moffat wrote:
> On Tue, 27 Apr 2004, Timothy Miller wrote:
>
>
>>
>>Ken Moffat wrote:
>>
>>
>>>So, despite the numbers shown by hdparm looking worse, when only one
>>>user is doing anything the performance is actually improved. I've no
>>>idea which changes have achieved this, but thanks to whoever were
>>>involved.
>>
>>
>>I've done tests using dd to and from the raw block device under 2.4 and
>>2.6. Memory size (kernel boot param mem=) doesn't seem to affect
>>performance, so I assume that means that dd to and from the raw block
>>device is unbuffered. When I compare read and write speeds between 2.4
>>and 2.6, 2.6 is definately slower. The last 2.6 kernel I tried this
>>with is 2.6.5.
>>
>
>
> Well, my original test used cp, sync, rm, sync. I've no statistics
> from running 2.4 on this box to compare against.
>

Based on my experience, cp and anything else that uses the filesystem
gets buffered. I can tell this because, without sync, the throughput
varies with memory size. Furthermore, I wanted to know raw throughput,
so I used a block device so I could eliminate filesystem overhead.

Reading and writing the block device does not seem to be buffered
because the run time is not affected by memory (host RAM) size. That
is, unless dd does an implicit sync.

The numbers I get when using dd to and from one of my drives under a 2.4
kernel with the drive connected to the on-board IDE controller are
roughly the same as published benchmarks.