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Re: [PATCH] Remove mfinfo[64] used by get_wchan()

To: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Subject: Re: [PATCH] Remove mfinfo[64] used by get_wchan()
From: Franck Bui-Huu <vagabon.xyz@gmail.com>
Date: Fri, 18 Aug 2006 09:50:57 +0200
Cc: vagabon.xyz@gmail.com, ralf@linux-mips.org, linux-mips@linux-mips.org
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Atsushi Nemoto wrote:
> On Thu, 17 Aug 2006 15:57:28 +0200, Franck Bui-Huu <vagabon.xyz@gmail.com> 
> wrote:
>> This array was used to 'cache' some frame info about scheduler
>> functions to speed up get_wchan(). This array was 1Ko size and
>> was only used when CONFIG_KALLSYMS was set but declared for all
>> configs.
>>
>> Rather than make the array statement conditional, this patches
>> removes this array and its uses. Indeed the common case doesn't
>> seem to use this array and get_wchan() is not a critical path
>> anyways.
> 
> It looks good basically, but a few fixes are required.
> 
>>  static int __init frame_info_init(void)
>>  {
>> -    int i;
>> +    unsigned long size = 0;
> 
> You must pass some non-zero size even if CONFIG_KALLSYMS was not set.
> Otherwise schedule_mfi will not be initialized as expected.  Actually,
> this is not a problem of this patch, but we missed this point on
> previous cleanups for the get_frame_info()...
> 

or maybe we can just fix get_frame_info() and make it more robust ?

>> +unsigned long get_wchan(struct task_struct *task)
>> +{
>> +    unsigned long stack_page = (unsigned long)task_stack_page(task);
> 
> This should be done after "if (!task ..." check.
> 
>> +    unsigned long pc = 0;
>> +#ifdef CONFIG_KALLSYMS
>> +    unsigned long sp = task->thread.reg29;
> 
> Same.  And you missed one stack level.
> 
>       sp = task->thread.reg29 + schedule_mfi.frame_size;
> 

Absolutely. I'll cook up a new patch and will send it today.

Thanks

                Franck

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