lkml.org 
[lkml]   [2006]   [Nov]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Subject[patch] Mark rdtsc as sync only for netburst, not for core2
From
Date
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/

\
 
 \ /
  Last update: 2006-11-28 11:31    [W:0.036 / U:11.996 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site