linux-kernel - Re: [patch] Mark rdtsc as sync only for netburst, not for core2

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Message-ID: <456D3F52.6040308@yahoo.com.au>
Date:	Wed, 29 Nov 2006 19:05:38 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Arjan van de Ven <arjan@...ux.intel.com>
CC:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org,
	akpm@...l.org
Subject: Re: [patch] Mark rdtsc as sync only for netburst, not for core2

Arjan van de Ven wrote:
> Zhang, Yanmin wrote:
> 
>> If it's a single processor, the go backwards issue doesn't exist. 
>> Below is
>> my patch based on Arjan's. It's against 2.6.19-rc5-mm2.
> 
> Hi,
> 
> this patch is incorrect
> 
>> --- linux-2.6.19-rc5-mm2_arjan/arch/x86_64/kernel/setup.c    
>> 2006-11-29 10:41:21.000000000 +0800
>> +++ linux-2.6.19-rc5-mm2_arjan_fix/arch/x86_64/kernel/setup.c    
>> 2006-11-29 10:42:28.000000000 +0800
>> @@ -861,7 +861,7 @@ 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);
>> -    if (c->x86 == 15)
>> +    if (c->x86 == 15 && num_possible_cpus() != 1)
>>          set_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
> 
> 
> first of all, you probably meant "|| num_possible_cpus() == 1"
> 
> but second of all, the core2 cpus are dual core so.. .what does it bring 
> you at all?

I guess you could boot with a UP kernel or maxcpus=1?

-- 
SUSE Labs, Novell Inc.
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