Re: Slow I/O on USB media after commit f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6

[Johannes Thumshirn <jthumshirn@suse.de>]

On Tue, Jul 02, 2019 at 12:46:45PM +0200, Andrea Vai wrote:
> Hi,
>   I have a problem writing data to a USB pendrive, and it seems
> kernel-related. With the help of Greg an Alan (thanks) and some
> bisect, I found out the offending commit being
> 
> commit f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6
> Author: Jens Axboe <axboe@kernel.dk>
> Date:   Thu Nov 1 16:36:27 2018 -0600
> 
>     scsi: kill off the legacy IO path
>     
>     This removes the legacy (non-mq) IO path for SCSI.
>     
> So, here I am to notify you about the problem and ask you if I can
> help in any way to work it out and fix it.
> 
> The problem is that if I copy a file from the internal SATA HD to the
> pendrive, it takes ~10 times to complete (in respect of the time
> needed with the patch reverted).
> 
> The test script, which I use to detect if the problem triggers or not,
> is:
> 
> #!/bin/bash
> logfile=...
> uname -a | tee -a $logfile
> echo -n "Begin: " | tee -a $logfile
> date | tee -a $logfile
> touch inizio
> SECONDS=0
> mount UUID="05141239-4ea5-494d-aa91-acd67db89ce5" /mnt/pendrive
> cp /NoBackup/buttare/testfile /mnt/pendrive
> umount /mnt/pendrive
> tempo=$SECONDS
> touch fine
> echo -n "...end: " | tee -a $logfile
> date | tee -a $logfile
> echo "It took $tempo seconds!" | tee -a $logfile
> 
> If I run the test with a 512MB file it takes >10min vs. half a minute.
> 
> The problem is still present in last tested git (cloned today in the
> morning).
> 
> You can see the previous discussion that lead to these results at
> 
> https://marc.info/?t=155922230700001&r=1&w=2

Hi,

Can you please check what IO scheduler you have set for your USB pendrive?

i.e. with:
cat /sys/block/$DISK/queue/scheduler

Thanks,
	Johannes
-- 
Johannes Thumshirn                            SUSE Labs Filesystems
jthumshirn@suse.de                                +49 911 74053 689
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