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[PATCH] x86-64: Mark rdtsc as sync only for netburst, not for core2

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On the Core2 cpus, the rdtsc instruction is not serializing (as defined
in the architecture reference since rdtsc exists) and due to the deep
speculation of these cores, it's possible that you can observe time go
backwards between cores due to this speculation. Since the kernel
already deals with this with the SYNC_RDTSC flag, the solution is
simple, only assume that the instruction is serializing on family 15...

The price one pays for this is a slightly slower gettimeofday (by a
dozen or two cycles), but that increase is quite small to pay for a
really-going-forward tsc counter.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andi Kleen <ak@suse.de>
[chrisw: backported to 2.6.18]
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
This commit is contained in:
Arjan van de Ven
2006-12-11 21:45:01 +01:00
committed by Chris Wright
parent 1dca7c2806
commit e4a835d383
1 changed files with 4 additions and 1 deletions
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arch/x86_64/kernel/setup.c
+4 -1
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@@ -1010,7 +1010,10 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
if ((c->x86 == 0xf && c->x86_model >= 0x03) ||
(c->x86 == 0x6 && c->x86_model >= 0x0e))
set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability);
set_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
if (c->x86 == 15)
set_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
else
clear_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
c->x86_max_cores = intel_num_cpu_cores(c);
srat_detect_node();