Re: [Regression] ext4: changes to mb_optimize_scan cause issues on Raspberry Pi

[Stefan Wahren]

Hi Jan,

Am 16.08.22 um 11:34 schrieb Jan Kara:
> Hi Stefan!
> So this is interesting. We can see the card is 100% busy. The IO submitted
> to the card is formed by small requests - 18-38 KB per request - and each
> request takes 0.3-0.5s to complete. So the resulting throughput is horrible
> - only tens of KB/s. Also we can see there are many IOs queued for the
> device in parallel (aqu-sz columnt). This does not look like load I would
> expect to be generated by download of a large file from the web.
>
> You have mentioned in previous emails that with dd(1) you can do couple
> MB/s writing to this card which is far more than these tens of KB/s. So the
> file download must be doing something which really destroys the IO pattern
> (and with mb_optimize_scan=0 ext4 happened to be better dealing with it and
> generating better IO pattern). Can you perhaps strace the process doing the
> download (or perhaps strace -f the whole rpi-update process) so that we can
> see how does the load generated on the filesystem look like? Thanks!

i didn't create the strace yet, but i looked at the source of 
rpi-update. At the end the download phase is a curl call to download a 
tar archive and pipe it directly to tar.

You can find the content list of the tar file here:

https://raw.githubusercontent.com/lategoodbye/mb_optimize_scan_regress/main/rpi-firmware-tar-content-list.txt

Best regards

> 								Honza