Re: 2.4 vs 2.6 USB mass storage device performance

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Tue, 20 Nov 2007, syed khader wrote:

> Hi,
>   We are evaluating performance of USB on both 2.4.25
> and 2.6.18.2 kernels on an EHCI mass storage device
> with a Seagat SCSI device on a Conexant's ARM11
> platform.
>   We see significant performace difference w.r.t 2.4
> and 2.6 on the same device:
> 
> On 2.6:
> #sg_dd /dev/sda dio=1 bs=1M count=100 flag=direct
> time=1
>   reports 12MBps
> while on 2.4
> #sg_dd /dev/sda dio=1 bs=1M count=100 flag=direct
> time=1
>   reports just 5.1MBps

It's good that 2.6 is faster than 2.4 and not slower!  :-)

>   I understand that 2.6 is more capable, but does 2.4
> has any limitations? Are there any patches available
> to improve the performance in 2.4?

Not exactly limitations.  2.6 has code to speed up large bulk 
transfers; this code isn't present in 2.4.  That probably accounts for 
much of the speed difference.

The code has never been ported back to 2.4, as far as I know.  Of 
course, if you want to do the porting yourself, please feel free.  I'll 
be happy to tell you what needs to be added or changed.

Alan Stern


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