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

[Ming Lei]

On Thu, Nov 07, 2019 at 07:59:44PM +0100, Andrea Vai wrote:
> [Sorry for the duplicate message, it didn't reach the lists due to
> html formatting]
> Il giorno gio 7 nov 2019 alle ore 08:54 Damien Le Moal
> <Damien.LeMoal@xxxxxxx> ha scritto:
> >
> > On 2019/11/07 16:04, Andrea Vai wrote:
> > > Il giorno mer, 06/11/2019 alle 22.13 +0000, Damien Le Moal ha scritto:
> > >>
> > >>
> > >> Please simply try your write tests after doing this:
> > >>
> > >> echo mq-deadline > /sys/block/<name of your USB
> > >> disk>/queue/scheduler
> > >>
> > >> And confirm that mq-deadline is selected with:
> > >>
> > >> cat /sys/block/<name of your USB disk>/queue/scheduler
> > >> [mq-deadline] kyber bfq none
> > >
> > > ok, which kernel should I test with this: the fresh git cloned, or the
> > > one just patched with Alan's patch, or doesn't matter which one?
> >
> > Probably all of them to see if there are any differences.
> 
> with both kernels, the output of
> cat /sys/block/sdh/queue/schedule
> 
> already contains [mq-deadline]: is it correct to assume that the echo
> command and the subsequent testing is useless? What to do now?

Another thing we could try is to use 'none' via the following command:

 echo none > /sys/block/sdh/queue/scheduler  #suppose 'sdh' points to the usb storage disk

Because USB storage HBA is single hw queue, which depth is 1. This way
should change to dispatch IO in the order of bio submission.

Andrea, could you switch io scheduler to none and update us if difference
can be made?

Thanks,
Ming