Comment # 76 on bug 1112963 from Jean Delvare

I have completed the bisection, and it points to:

commit 2a9e851cb5c132f0cba9bcc25822f0a25af23179
Author: Jiri Slaby
Date:   Wed Aug 22 11:34:05 2018 +0200

    drm/drivers: add support for using the arch wc mapping API
    (git-fixes).

which corresponds to
patches.suse/drm-drivers-add-support-for-using-the-arch-wc-mappin.patch, which
is upstream commit 7cf321d118a825c1541b43ca45294126fd474efa. That is the same
patch that Takashi reverted in comment #52. The kernel from comment #52 _does_
solve the performance regression I'm seeing in the console. However Edward says
in comment #53 that it does not solve his problem. I have to admit I'm rather
confused at this point.

One possibility is that we in fact have 2 different bugs, one affecting the
console, and one affecting X.org. But I have a hard time believing that. If
anyone has a better explanation, I'm all ears.

My test case is: I switch to a text console (Ctrl+Alt+F2), log in as root, and
measure the time it takes to "cat" a relatively large text file. Without the
patch mentioned above, it takes around 68 seconds; with the patch, it takes
around 128 seconds.

Edward, what tests are you doing exactly to determine which kernels are good
and which are bad?