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SubjectSluggishness on a GEM system due to SELinux's sidtab_search_context() as well as get_unmapped_area()
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Hello,

I'm noticing significant sluggishness when switching into a workspace
where Evolution is running.

My kernel is Fedora 12's 2.6.32.16-150.fc12.x86_64 (I know it is
old...), and the open source radeon (r600) driver is used. Oprofile
shows the follows:

CPU: Core 2, speed 2003 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a
unit mask of 0x00 (Unhalted core cycles) count 100000
Counted INST_RETIRED_ANY_P events (number of instructions retired) with
a unit mask of 0x00 (No unit mask) count 100000
samples % samples % image name app name
symbol name
126807 31.2201 38744 28.3866 vmlinux Xorg
(deleted) find_vma
48661 11.9804 3474 2.5453 vmlinux Xorg
(deleted) mls_compute_sid
41806 10.2927 5700 4.1762 vmlinux Xorg
(deleted) sidtab_search_context
11888 2.9268 4234 3.1021 Xorg (deleted) Xorg
(deleted) /usr/bin/Xorg (deleted)
8660 2.1321 1589 1.1642 drm Xorg
(deleted) /drm
6228 1.5333 6773 4.9624 radeon Xorg
(deleted) /radeon
6214 1.5299 1832 1.3423 libc-2.11.2.so (deleted) Xorg
(deleted) /lib64/libc-2.11.2.so (deleted)
5542 1.3644 4929 3.6113
libpixman-1.so.0.16.6.#prelink#.3I5wow (deleted) Xorg
(deleted) /usr/lib64/libpixman-1.so.0.16.6.#prelink#.3I5wow
(deleted)
4149 1.0215 1776 1.3012 libexa.so Xorg
(deleted) /usr/lib64/xorg/modules/libexa.so
4140 1.0193 640 0.4689 vmlinux oprofiled
mls_compute_sid
3183 0.7837 847 0.6206 vmlinux Xorg
(deleted) arch_get_unmapped_area_topdown
...

Although I haven't looked into it, presumably Evolution is asking the X
server to create and map a lot of TTM objects (pixmaps?). The creation
of each object uses shmem_file_setup() and thus necessitates SELinux
calls, and since the X process already has a lot of mappings (one
mapping for each XRender glyph it seems, with "wc -l /proc/`pgrep
Xorg`/maps" returning 6766), the mapping part could also be slow.

I think the slowness of find_vma is related to
https://bugzilla.kernel.org/show_bug.cgi?id=17531 . mls_compute_sid()
did a linear search over the range transition rules and was therefore
slow, but more recent kernels use a hash table so this problem has been
solved. Another offender is sidtab_search_context() used to convert a
SELinux context back into an sid, which is also a linear search as there
is only a sid => context hash table, and I haven't seen any recent
changes in this area.

Please CC me as I'm not subscribed.

r6144



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