Re: [PATCH v2 1/2] x86: Add cpu_detect_cache_sizes() to init_intel(), add Quark to legacy_cache()

["Bryan O'Donoghue" <pure.logic@nexus-software.ie>]

On 06/10/14 10:55, Thomas Gleixner wrote:
>> +	 */
>> +	if (c->x86_cache_size == 0)
>> +		l2 = init_intel_cacheinfo(c);
>> +	else
>> +		l2 = c->x86_cache_size;
>
> Looking a bit deeper. This wont work because cpu_detect_cache_sizes()
> will set c->x86_cache_size for all cpus with extended_cpuid_level >=
> 0x80000005, which is the case for everything modern. So this results
> in init_intel_cacheinfo() not being called anymore.

True.

Missed that one.

> So we might need the following conditional:
>
> 	l2 = init_intel_cacheinfo(c);
> +	if (!c->x86_cache_size) {
> +		cpu_detect_cache_sizes(c);
> +		l2 = c->x86_cache_size;
> +	}

Yes - that'll work better.

Also - it only forces a conditional branch - so fewer extra cycles for 
everybody !Quark and !Tualatin - which is preferential. Will incorporate.


Best,
Bryan