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Synchronize rdtsc instructions

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The CPU can arbitrarily reorder calls to rdtsc, significantly
reducing the precision of timing using the CPUs time stamp counter.
Unfortunately the method of synchronizing rdtsc is different
on AMD and Intel CPUs. There is a generic method, using the cpuid
instruction, but that uses up a lot of registers, and is very slow.
Hence, use the correct lfence/mfence instructions (for CPUs that
we know support it)

Change-Id: I17ecb48d283f38f23148c13159aceda704c64ea5
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/1422
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Tested-by: build bot (Jenkins)
This commit is contained in:
Stefan Reinauer
2012-08-07 14:44:51 -07:00
committed by Stefan Reinauer
parent 4c29d7f27d
commit 0db6820b10
10 changed files with 40 additions and 4 deletions
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16
src/cpu/x86/Kconfig
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@@ -23,6 +23,22 @@ config TSC_CALIBRATE_WITH_IO
bool
default n
config TSC_SYNC_LFENCE
bool
default n
help
The CPU driver should select this if the CPU needs
to execute an lfence instruction in order to synchronize
rdtsc. This is true for all modern AMD CPUs.
config TSC_SYNC_MFENCE
bool
default n
help
The CPU driver should select this if the CPU needs
to execute an mfence instruction in order to synchronize
rdtsc. This is true for all modern Intel CPUs.
config XIP_ROM_SIZE
hex
default ROM_SIZE if ROMCC