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lib/ovs-atomic: Native support for 32-bit 586 with GCC.
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XenServer runs OVS in dom0, which is a 32-bit VM.  As the build
environment lacks support for atomics, locked pthread atomics were
used with considerable performance hit.

This patch adds native support for ovs-atomic with 32-bit Pentium and
higher CPUs, when compiled with an older GCC.  We use inline asm with
the cmpxchg8b instruction, which was a new instruction to Intel
Pentium processors.  We do not expect anyone to run OVS on 486 or older
processor.

cmap benchmark before the patch on 32-bit XenServer build (uses
ovs-atomic-pthread):

$ tests/ovstest test-cmap benchmark 2000000 8 0.1
Benchmarking with n=2000000, 8 threads, 0.10% mutations:
cmap insert:   8835 ms
cmap iterate:   379 ms
cmap search:   6242 ms
cmap destroy:  1145 ms

After:

$ tests/ovstest test-cmap benchmark 2000000 8 0.1
Benchmarking with n=2000000, 8 threads, 0.10% mutations:
cmap insert:    711 ms
cmap iterate:    68 ms
cmap search:    353 ms
cmap destroy:   209 ms

Signed-off-by: Jarno Rajahalme <[email protected]>
Acked-by: Ben Pfaff <[email protected]>
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Jarno Rajahalme committed Aug 5, 2014
1 parent f31841d commit 105a929
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1 change: 1 addition & 0 deletions lib/automake.mk
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Expand Up @@ -150,6 +150,7 @@ lib_libopenvswitch_la_SOURCES = \
lib/ovs-atomic-flag-gcc4.7+.h \
lib/ovs-atomic-gcc4+.h \
lib/ovs-atomic-gcc4.7+.h \
lib/ovs-atomic-i586.h \
lib/ovs-atomic-locked.c \
lib/ovs-atomic-locked.h \
lib/ovs-atomic-pthreads.h \
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