Re: [RFC][PATCH] Add do_not_call_when_idle option to timer and workqueue

[Avi Kivity <avi@argo.co.il>]

Andrew Morton wrote:
>> Index: linux-2.6.19-rc-mm/include/linux/timer.h
>> ===================================================================
>> --- linux-2.6.19-rc-mm.orig/include/linux/timer.h	2006-11-13 15:06:26.000000000 -0800
>> +++ linux-2.6.19-rc-mm/include/linux/timer.h	2006-11-13 16:01:03.000000000 -0800
>> @@ -8,6 +8,8 @@
>>  
>>  struct tvec_t_base_s;
>>  
>> +#define TIMER_FLAG_NOT_IN_IDLE	(0x1)
>> +
>>  struct timer_list {
>>  	struct list_head entry;
>>  	unsigned long expires;
>> @@ -16,6 +18,7 @@
>>  	unsigned long data;
>>  
>>  	struct tvec_t_base_s *base;
>> +	int	flags;
>>  #ifdef CONFIG_TIMER_STATS
>>     
>
> Adding a new field to the timer_list is somewhat of a hit - this is going
> to make an awful lot of data structures a bit larger.  Some of which we
> allocate a large number of.
>
> I think we could justfy getting nasty and using the LSB of
> timer_list.function for this..
>
>   

The lsb of a function pointer is used in variable length instruction 
processors (such as x86 when optimizing for size).  The msb is constant 
though.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.