Messages in this thread Patch in this message | | | Subject | [patch] Mark rdtsc as sync only for netburst, not for core2 | From | Arjan van de Ven <> | Date | Tue, 28 Nov 2006 11:28:28 +0100 |
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Hi,
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>
--- linux-2.6.18/arch/x86_64/kernel/setup.c.org 2006-11-28 11:22:08.000000000 +0100 +++ linux-2.6.18/arch/x86_64/kernel/setup.c 2006-11-28 11:22:50.000000000 +0100 @@ -854,7 +854,10 @@ static void __cpuinit init_intel(struct set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability); if (c->x86 == 6) set_bit(X86_FEATURE_REP_GOOD, &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(); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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