From: jason77.wang@gmail.com (Hui Wang)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] ARM: fix cpu_relax() in case of doing dmb
Date: Fri, 24 Aug 2012 09:10:43 +0800 [thread overview]
Message-ID: <5036D493.7050204@gmail.com> (raw)
In-Reply-To: <20120823104356.GA13622@mudshark.cambridge.arm.com>
Will Deacon wrote:
> On Wed, Aug 22, 2012 at 03:52:18PM +0100, Shawn Guo wrote:
>
>> diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
>> index 99afa74..7cc67ce 100644
>> --- a/arch/arm/include/asm/processor.h
>> +++ b/arch/arm/include/asm/processor.h
>> @@ -80,7 +80,14 @@ extern void release_thread(struct task_struct *);
>> unsigned long get_wchan(struct task_struct *p);
>>
>> #if __LINUX_ARM_ARCH__ == 6 || defined(CONFIG_ARM_ERRATA_754327)
>> -#define cpu_relax() smp_mb()
>> +#define cpu_relax() do { \
>> + asm("nop"); \
>> + asm("nop"); \
>> + asm("nop"); \
>> + asm("nop"); \
>> + asm("nop"); \
>>
>
> Can you use nop() instead of the explicit asm? Also, I think we should try
> and use some methodology on deciding the number of nops to insert. Without
> having a full handle on the problem at the moment, it would seem that we
> need at least NR_CPUS worth (since the number of spinning secondaries is
> NR_CPUS-1 and they may execute their barriers in lock-step).
>
Your concern sounds reasonable, but i did a test, the result show there
is no explicit relation between NR_CPUS and the number of nop needed.
NR_CPUS = 4 and NR_CPUS = 2 need at least the same number of nop.
Regards,
Hui.
> Will
>
>
prev parent reply other threads:[~2012-08-24 1:10 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-22 14:52 [PATCH] ARM: fix cpu_relax() in case of doing dmb Shawn Guo
2012-08-23 2:47 ` Hui Wang
2012-08-23 10:23 ` Dirk Behme
2012-08-23 10:43 ` Will Deacon
2012-08-23 13:58 ` Shawn Guo
2012-08-23 18:31 ` Jon Medhurst (Tixy)
2012-08-24 1:15 ` Shawn Guo
2012-08-24 9:14 ` Jon Medhurst (Tixy)
2012-08-24 1:10 ` Hui Wang [this message]
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