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

[Ming Lei]

On Mon, Nov 11, 2019 at 11:50:49AM +0100, Andrea Vai wrote:
> Il giorno dom, 10/11/2019 alle 06.28 +0800, Ming Lei ha scritto:
> > 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?
> 
> Of course I would to it, but I see that with the "good" kernel the
> output of "cat /sys/block/sdf/queue/scheduler" (yes, now it's sdf) is
> 
> noop deadline [cfq]

Not sure if cfq makes a difference, and I guess you may get same result
with noop or deadline. However, if you only see good write performance with
cfq, you may try 'bfq' and see if it works as cfq.

> 
> , i.e. it doesn't show "none". Does it matter? (sorry if it's a silly
> question)

We are talking about new kernel in which there can't be 'noop deadline [cfq]'
any more. And you should see the following output from '/sys/block/sdf/queue/scheduler'
in the new kernel:

	[mq-deadline] kyber bfq none


thanks,
Ming