Re: Slow I/O on USB media

From: Andrea Vai <andrea.vai@unipv.it>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org, stern@rowland.harvard.edu
Subject: Re: Slow I/O on USB media
Date: Thu, 06 Jun 2019 16:00:52 +0200	[thread overview]
Message-ID: <b159e1518b670d4b0126c7671c30c8c3cb8fffbc.camel@unipv.it> (raw)
In-Reply-To: <20190605173902.GE27700@kroah.com>

Il giorno mer, 05/06/2019 alle 19.39 +0200, Greg KH ha scritto:
> On Wed, Jun 05, 2019 at 06:23:58PM +0200, Andrea Vai wrote:
> [...]
> 
> > Anyway, I know that I can do all of this in a better way, and will
> let
> > you know.
> 
> Yes, please do so, your steps above do not show much.

Here I am with another question.
What I have done so far:

- booted with the last kernel I know to be working (4.20.13-
200.fc29.x86_64, installed from Fedora repos), checked that test runs
fine (2min to copy)
- marked "git bisect good v4.20.13"
- built the latest stable version:
  - git clone https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
  - cp -v /boot/config-$(uname -r) .config
  - make -j4 && make modules_install && make install && grub2-mkconfig -o /boot/grub2/grub.cfg
  - grubby --set-default /boot/vmlinuz-5.2.0-rc3 (the last regular file listed in "ls -lrt /boot/v*")
- rebooted with kernel 5.2.0-rc3, ran the test, took 49min to copy
(!), thus marked "git bisect bad"
- built again, and it turns out to be 4.20.0 (why is it earlier than
4.20.13?), rebooted with 4.20.0, ran the test and it took more than 15
minutes so I killed the cp process, and marked it BAD, and obtained:

The merge base 8fe28cb58bcb235034b64cbbb7550a8a43fd88be is bad.
This means the bug has been fixed between
8fe28cb58bcb235034b64cbbb7550a8a43fd88be and
[0f7c162c1df596e0bba04c26fc9cc497983bf32b].

The output of "git bisect log" is:

git bisect start
# good: [0f7c162c1df596e0bba04c26fc9cc497983bf32b] Linux 4.20.13
git bisect good 0f7c162c1df596e0bba04c26fc9cc497983bf32b
# bad: [f2c7c76c5d0a443053e94adb9f0918fa2fb85c3a] Linux 5.2-rc3
git bisect bad f2c7c76c5d0a443053e94adb9f0918fa2fb85c3a
# bad: [8fe28cb58bcb235034b64cbbb7550a8a43fd88be] Linux 4.20
git bisect bad 8fe28cb58bcb235034b64cbbb7550a8a43fd88be

I can understand that the bug was present before 4.20.13 (is that
reasonable?), but how can I tell bisect to start at 4.20.13, which I
know for sure to be working, and not from 4.20.0, which I actually
don't care about?

I am afraid I am missing something obvious, sorry

Thank you very much,
Andrea