Re: Software RAID checksum performance on 24 disks not even close to kernel reported

[Brad Campbell <lists2009@fnarfbargle.com>]

On 06/06/12 02:44, Ole Tange wrote:
> On Tue, Jun 5, 2012 at 1:29 PM, Igor M Podlesny<for.poige+lsr@gmail.com>  wrote:
>> On 5 June 2012 15:47, Ole Tange<ole@tange.dk>  wrote:
>>> On Tue, Jun 5, 2012 at 5:39 AM, Igor M Podlesny<for.poige+lsr@gmail.com>  wrote:
>>>> On 5 June 2012 07:14, Ole Tange<ole@tange.dk>  wrote:
>>>> […]
>>>>> I tested this by creating 24 devices in RAM, used different chunk
>>>>> sizes, and then copied the linux kernel source. Test script can be
>>>>> found on http://oletange.blogspot.dk/2012/05/software-raid-performance-on-24-disks.html
> :
>>    Wanna try CONFIG_MULTICORE_RAID456? :-)
>
> If the kernel can checksum 6196 MB/s why would I need
> CONFIG_MULTICORE_RAID456? Please elaborate on why you think that is
> needed.

I'd have thought there was a significant difference between the test 
generating that figure (being a large, single block being checksummed) 
and shunting around blocks from 20 odd block devices, arranging them and 
checksumming them.

I'm not debating the validity of your tests at all, however I do 
question your assertion than a single raid6 thread should even get close 
to that theoretical figure when actually doing real work.

Why not do as the man suggested and enable CONFIG_MULTICORE_RAID456 and 
see what happens?

Regards,
Brad
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