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My recent measurement shows that CPU_DISABLE_CMPXCHG is no longer necessary

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with VmWare 4.x. At least with VmWare version 4.5.2, i386 version of
atomic_cmpset_int() is about 30 times slower than non-i386 version. It
makes this delta a good 5.3 MFC candidate, since otherwise it will
mislead users who run FreeBSD under modern VmWare otherwise.
This commit is contained in:
Maxim Sobolev 2004-08-23 15:55:03 +00:00
parent bd41e9ea59
commit c1466d61d9
1 changed files with 5 additions and 3 deletions
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8
sys/i386/conf/NOTES
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@ -101,9 +101,11 @@ cpu I686_CPU # aka Pentium Pro(tm)
# I/O device(s).
#
# CPU_DISABLE_CMPXCHG disables the CMPXCHG instruction on > i386 IA32
# machines. VmWare seems to emulate this instruction poorly, causing
# the guest OS to run very slowly. Enabling this with an SMP kernel
# will cause the kernel to be unusable.
# machines. VmWare 3.x seems to emulate this instruction poorly, causing
# the guest OS to run very slowly. This problem appears to be fixed in
# VmWare 4.x, at least in version 4.5.2, so that enabling this option with
# VmWare 4.x will result in locking operations to be 20-30 times slower.
# Enabling this with an SMP kernel will cause the kernel to be unusable.
#
# CPU_DISABLE_SSE explicitly prevents I686_CPU from turning on SSE.
#