Re: mass storage behaviour

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Hi Paul,

Good to see you're still hanging around.

On 10/5/2015 3:38 PM, Paul Zimmerman wrote:
> On Mon, 5 Oct 2015, Alan Stern wrote:
>> On Mon, 5 Oct 2015, Paul Jones wrote:
>>
>>>> Increasing the max_sectors_kb value, on the other hand, might remove
>>>> overhead by allowing a higher percentage of the transfer to consist of
>>>> real data as opposed to CBW and CSW packets.  This depends to some
>>>> extent on other factors (such as whether the memory pages are
>>>> contiguous, allowing for larger transfers), but it can't hurt.
>>>
>>> I tried changing the max_sectors_kb to 64 with 64k block size in dd and it’s transferring at the same \
>> speed.
>>
>> That's a decrease, not an increase.  Try changing it to 1024 or more.
>>
>>> I verified using usbmon and it then indeed requests 64k in each request.
>>> Increasing the dd block size to 240k doesn’t change the transfer speed either, and it keeps using \
>>> alternating 120k/8k requests. Increasing the dd block size to 1M doesn’t change the transfer speed \
>>> either, although I get sequences of 2x 120k followed by 1x 16k requests.
>>
>> The dd block size makes no difference at all, because the kernel
>> aggregates the requests from dd.
> 
> In my experience, you need to do at least the following to get max
> performance from the mass storage gadget:
> 
> - Use Windows 8 or higher on the host. It's much faster than Linux.
> - Put the backing file for the mass storage gadget on a tmpfs.
> - Increase FSG_BUFLEN (in

Speaking of which...

I found this old patch to set the FSG_BUFLEN. Any idea why it never
got merged?

http://marc.info/?l=linux-usb&m=138722294117498&w=2

Regards,
John


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