Re: Subject: [PATCH] [PATCH] time: tick-sched: use bool for tick_stopped

[yuankuiz]

On 2018-04-10 03:55 PM, Thomas Gleixner wrote:
> On Tue, 10 Apr 2018, yuankuiz@xxxxxxxxxxxxxx wrote:
>
> > From: John Zhao <yuankuiz@xxxxxxxxxxxxxx>
> >
> > Variable tick_stopped returned by tick_nohz_tick_stopped
> > can have only true / forse values. Since the return type
> > of the tick_nohz_tick_stopped is also bool, variable
> > tick_stopped nice to have data type as bool in place of int.
>
> The data type is not int.
[ZJ] Yes. Per newest tip in branch of linux-pm-cpuidle, it is unsigned 
int with 1 bit in width.
There is typo in commit message, "int" at here should be "unsigned int"

> It's part of an integer bitfield and occupies
> exactly one bit of storage, while bool has an architecture dependend 
> size
> and is at least 1 byte, i.e. 8 bit. So with alignment effects you grew 
> the
> size of the data structure and therefore the cache foot print.
[ZJ] So, 1 bit in width is specified as:
+	bool				tick_stopped	: 1;
     This patch is based on the linux-pm-cpuidle branch which has
already gathered available space in the structure of tick_sched.

> This is not about 'nice to have' ....
>
> Thanks,
>
> 	tglx