Re: Slow I/O on USB media

[Alan Stern <stern@rowland.harvard.edu>]

On Wed, 5 Jun 2019, Andrea Vai wrote:

> Hi,
> Il giorno mar, 04/06/2019 alle 07.43 +0200, Greg KH ha scritto:
> > On Mon, Jun 03, 2019 at 01:13:48PM +0200, Andrea Vai wrote:
> > > Il giorno gio, 30/05/2019 alle 06.25 -0700, Greg KH ha scritto:
> > > > [...]
> > > Hi,
> > > 
> > > > Any chance you can use 'git bisect' to find the offending
> > commit?
> > > Yes, I am doing it as I managed to build the kernel from source
> > 
> > Great!  What did you find?
> 
> # first bad commit: [534903d60376b4989b76ec445630aa10f2bc3043]
> drm/atomic: Use explicit old crtc state in
> drm_atomic_add_affected_planes()
> 
> By the way, as I am not expert, is there a way to double-check that I
> bisected correctly? (such as, e.g., test with the version before this
> one, and then with this commit applied?)

That is exactly the way to do it: Build a kernel from that commit and 
see that it fails, then revert the commit and see that the resulting 
kernel succeeds.

(Note: The notion of "version before" doesn't have a firm meaning in 
the kernel, because some commits have multiple parents.  The best way 
to see if a single commit caused a change is to do what I said above: 
revert the commit and see what happens.)

Incidentally, it seems very unlikely that a commit for the drm 
subsystem would have any effect on the behavior of a USB storage 
device.

Alan Stern