Re: [PATCH u-boot-marvell 00/13] Yet another kwboot improvements

Pali Rohár
2021-10-28T11:04:48Z

On Thursday 28 October 2021 08:16:24 Stefan Roese wrote:
> On 27.10.21 23:03, Pali Rohár wrote:
> > On Wednesday 27 October 2021 17:27:41 Stefan Roese wrote:
> > > Still I see no speed change. But this is a different story...
> >
> > Could you try to upload some file in u-boot via xmodem at different
> > speeds? E.g. via loadx command:
> >
> > loadx <addr> 921600
> >
> > and
> >
> > loadx <addr> 115200
>
> loadx & loady are producing nearly the same numbers on my Armada XP
> target for download (slow of cause). This is really strange.

Ok. So it means that the issue should not be in kwboot, if also U-Boot
xmodem implementation is affected.

> I also tested with "normal" console actions (logging) with higher
> baudrates. Here these numbers:
>
> time md 2000000 10000:
>
> 115200 baud:
> time: 1 minutes, 32.694 seconds
>
> 921600 baud:
> time: 11.587 seconds
>
> 92.7s vs 11.6s -> factor ~8. Which is exactly the baudrate difference.
> So at least here I see a speed difference, which means that the USB
> UART converter must be working in general. I really have no idea right
> now to explain, why this does not any speed differences while
> downloading.

So this means that USB-UART converter must work also on higher speeds.

My idea is that there is some significant overhead on USB-UART when
accessing either RX or TX queue. xmodem protocol is: send 132 bytes,
wait for 1 byte reply, send another 132 bytes, wait again for 1 byte
reply, ... So if USB-UART has internal overhead which cause that every
byte is postponed by some delay then it would mean that xmodem is most
time just waiting, meaning overhead is applied for every one 132-byte
long packet. Test with md cause continuous stream of data, therefore
such overhead is applied only at beginning of the md transfer.

Similar issues with can observed also on high speed networks were is
very big latency when using protocols where each small packet has to be
acknowledged. TCP is using windowing to prevent such kind of issues.

And kermit protocol too via its streaming mode. So kermit transfer could
prove if this is really that issue.

Anyway, I have looked at your strace output again and I saw that there
is a long gap after tcdrain() and end of the read(). So if kernel
implements tcdrain() for your USB-UART hw it means that it take too much
time to receive reply byte from USB-UART hw to the kernel. So it could
be another indication of that overhead.

> > And compare if xmodem transfer is in U-Boot faster or not. Ideally also
> > try via kermit protocol at different speeds as kernel supports
> > streaming.
>
> I'm currently struggling to get gkermit working on my Ubuntu machine -
> so no numbers here yet, sorry.

In U-Boot console call:

loadb _addr_

And then quit terminal emulator used for U-Boot /dev/ttyUSBX device.
Then run gkermit with following arguments:

gkermit -i -X -s _file_to_send_ < /dev/ttyUSBX > /dev/ttyUSBX

(redirecting both stdin and stdout is required)

After successful transfer gkermit exit. BEWARE that gkermit does not
print any progress information and neither any error. So do not kill
gkermit via CTRL+C prematurely. You can use "time gkermit ..." for
measuring total transfer time.

If you are going to use different speed than 115200 in u-boot run:

loadb _addr_ _speed_

And then on host start gkermit with more commands around:

stty -F /dev/ttyUSBX _speed_
printf '\015' > /dev/ttyUSBX
gkermit -i -X -s _file_to_send < /dev/ttyUSBX > /dev/ttyUSBX
sleep 0.5
stty -F /dev/ttyUSBX 115200
printf '\033' > /dev/ttyUSBX

Due to absence of progress bar and error information I'm using ckermit
application for kermit file transfers. But for testing purposes is
gkermit application here also fine.

> > This could verify if issue is in kwboot or in USB-UART/kernel.
>
> Makes sense.
>
> Thanks,
> Stefan