[Bug 84794] New: [snb] GTT go slow

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=84794

            Bug ID: 84794
           Summary: [snb] GTT go slow
           Product: DRI
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: critical
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: chris at chris-wilson.co.uk
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

commit ea8596bb2d8d37957f3e92db9511c50801689180
Author: Masami Hiramatsu <masami.hiramatsu.pt at hitachi.com>
Date:   Thu Jul 18 20:47:53 2013 +0900

    kprobes/x86: Remove unused text_poke_smp() and text_poke_smp_batch()
functions

    Since introducing the text_poke_bp() for all text_poke_smp*()
    callers, text_poke_smp*() are now unused. This patch basically
    reverts:

      3d55cc8a058e ("x86: Add text_poke_smp for SMP cross modifying code")
      7deb18dcf047 ("x86: Introduce text_poke_smp_batch() for batch-code
modifying")

    and related commits.

    This patch also fixes a Kconfig dependency issue on STOP_MACHINE
    in the case of CONFIG_SMP && !CONFIG_MODULE_UNLOAD.

    Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt at hitachi.com>
    Reviewed-by: Jiri Kosina <jkosina at suse.cz>
    Cc: H. Peter Anvin <hpa at linux.intel.com>
    Cc: Steven Rostedt <rostedt at goodmis.org>
    Cc: Jason Baron <jbaron at akamai.com>
    Cc: yrl.pp-manager.tt at hitachi.com
    Cc: Borislav Petkov <bpetkov at suse.de>
    Link:
http://lkml.kernel.org/r/20130718114753.26675.18714.stgit@mhiramat-M0-7522
    Signed-off-by: Ingo Molnar <mingo at kernel.org>

(bisected and manually checked)

This patch appears to make repeated access through the GTT extremely slow
(roughly equivalent to uc access I would say). This is demonstrated by
igt/gem_gtt_speed, and affects everything using X and mesa

???

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