Re: [PATCH 3/3] KVM: x86/vPMU: Add lazy mechanism to release perf_event per vPMC

[Like Xu]

Hi Peter,

On 2019/10/1 16:23, Peter Zijlstra wrote:
> On Mon, Sep 30, 2019 at 03:22:57PM +0800, Like Xu wrote:
> > +	union {
> > +		u8 event_count :7; /* the total number of created perf_events */
> > +		bool enable_cleanup :1;
>
> That's atrocious, don't ever create a bitfield with base _Bool.

I saw this kind of usages in the tree such as "struct 
arm_smmu_master/tipc_mon_state/regmap_irq_chip".

I'm not sure is this your personal preference or is there a technical
reason such as this usage is not incompatible with union syntax?

My design point is to save a little bit space without introducing
two variables such as "int event_count & bool enable_cleanup".

One of the alternatives is to introduce "u8 pmu_state", where the last 
seven bits are event_count for X86_PMC_IDX_MAX and the highest bit is 
the enable_cleanup bit. Are you OK with this ?

By the way, is the lazy release mechanism looks reasonable to you?

> > +	} state;