[Nouveau] "enable ctxprog xfer only when we need it to save power" introduces big performance regression

[Marcin Slusarz]

Hi

I've bisected pretty big performance regression (nv92):

$ git bisect good
b2737681d5442f05ab6419e05468c3d2511a5ced is the first bad commit
commit b2737681d5442f05ab6419e05468c3d2511a5ced
Author: Martin Peres <martin.peres at ensi-bourges.fr>
Date:   Sat Jul 30 23:08:45 2011 +0200

    drm/nv50/gr: enable ctxprog xfer only when we need it to save power

    This patch adds instructions to ctxprog and by doing, impacts context
    switching performance.  My testcase showed a 1% performance cost using
    glxgears that is a context-switch bound application.

    Please test and report bugs/performance/power/other.

    Many thanks to Maxim Levitsky for his dedicated work on lowering power
    consumption with nouveau.

    More patches are coming thanks to his work:

    https://bugs.freedesktop.org/show_bug.cgi?id=37922

    Signed-off-by: Martin Peres <martin.peres at ensi-bourges.fr>
    Signed-off-by: Ben Skeggs <bskeggs at redhat.com>

:040000 040000 3fcd1388cf04c71cb7a11f29f7be6033c948f119 418a527ee5970eabaa0eb6f8cb3dc96b4da523ea M      drivers

The numbers are (FPS):
nexuiz:            61 ->   49 (-19%)
xonotic:           59 ->   37 (-37%)
openarena:        163 ->  127 (-22%)
world of padman:  242 ->  181 (-25%)
warsow:            91 ->   61 (-32%)
glxgears:        1198 -> 1107 (- 7%)

Now, what can we do about it?

Marcin