Virtualization - Mar 2021 - [PATCH v6 02/12] x86/paravirt: switch time pvops functions to use static_call()

On Tue, Mar 09, 2021 at 02:48:03PM +0100, Juergen Gross
wrote:
> @@ -167,6 +168,17 @@ static u64 native_steal_clock(int cpu)
>  	return 0;
>  }
>  
> +DEFINE_STATIC_CALL(pv_steal_clock, native_steal_clock);
> +DEFINE_STATIC_CALL(pv_sched_clock, native_sched_clock);
> +
> +bool paravirt_using_native_sched_clock = true;
> +
> +void paravirt_set_sched_clock(u64 (*func)(void))
> +{
> +	static_call_update(pv_sched_clock, func);
> +	paravirt_using_native_sched_clock = (func == native_sched_clock);
> +}
What's the point of this function if there's a global
paravirt_using_native_sched_clock variable now?

Looking how the bit of information whether native_sched_clock is used,
is needed in tsc.c, it probably would be cleaner if you add a

set_sched_clock_native(void);

or so, to tsc.c instead and call that here and make that long var name a
a shorter and static one in tsc.c instead.

Hmm?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

On 09.03.21 19:57, Borislav Petkov wrote:
> On Tue, Mar 09, 2021 at 02:48:03PM +0100, Juergen Gross wrote:
>> @@ -167,6 +168,17 @@ static u64 native_steal_clock(int cpu)
>>   	return 0;
>>   }
>>   
>> +DEFINE_STATIC_CALL(pv_steal_clock, native_steal_clock);
>> +DEFINE_STATIC_CALL(pv_sched_clock, native_sched_clock);
>> +
>> +bool paravirt_using_native_sched_clock = true;
>> +
>> +void paravirt_set_sched_clock(u64 (*func)(void))
>> +{
>> +	static_call_update(pv_sched_clock, func);
>> +	paravirt_using_native_sched_clock = (func == native_sched_clock);
>> +}
> 
> What's the point of this function if there's a global
> paravirt_using_native_sched_clock variable now?
It is combining the two needed actions: update the static call and
set the paravirt_using_native_sched_clock boolean.
> Looking how the bit of information whether native_sched_clock is used,
> is needed in tsc.c, it probably would be cleaner if you add a
> 
> set_sched_clock_native(void);
> 
> or so, to tsc.c instead and call that here and make that long var name a
> a shorter and static one in tsc.c instead.
I need to transfer a boolean value, so it would need to be

set_sched_clock_native(bool state);

In the end the difference is only marginal IMO.

Just had another idea: I could add a function to static_call.h for
querying the current function. This would avoid the double book keeping
and could probably be used later when switching other pv_ops calls to
static_call, too (e.g. pv_is_native_spin_unlock()).

What do you think?


Juergen
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OpenPGP_0xB0DE9DD628BF132F.asc
Type: application/pgp-keys
Size: 3091 bytes
Desc: not available
URL:
<http://lists.linuxfoundation.org/pipermail/virtualization/attachments/20210310/ab779873/attachment-0001.bin>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OpenPGP_signature
Type: application/pgp-signature
Size: 495 bytes
Desc: OpenPGP digital signature
URL:
<http://lists.linuxfoundation.org/pipermail/virtualization/attachments/20210310/ab779873/attachment-0001.sig>