Re: [PATCH v4 7/7] selftests/resctrl: Adjust effective L3 cache size when SNC enabled

[Tony Luck]

On Mon, Aug 28, 2023 at 10:06:32AM -0700, Reinette Chatre wrote:
> Hi Tony,
> 
> On 8/25/2023 10:56 AM, Tony Luck wrote:
> > On Fri, Aug 11, 2023 at 10:33:43AM -0700, Reinette Chatre wrote:
> >> Hi Tony,
> >>
> >> On 7/22/2023 12:07 PM, Tony Luck wrote:
> 
> ...
> 
> >>> @@ -190,6 +245,8 @@ int get_cache_size(int cpu_no, char *cache_type, unsigned long *cache_size)
> >>>  			break;
> >>>  	}
> >>>  
> >>> +	if (cache_num == 3)
> >>> +		*cache_size /= snc_ways();
> >>>  	return 0;
> >>>  }
> >>>  
> >>
> >> I am surprised that this small change is sufficient. The resctrl
> >> selftests are definitely not NUMA aware and the CAT and CMT tests
> >> are not taking that into account when picking CPUs to run on. From
> >> what I understand LLC occupancy counters need to be added in this
> >> scenario but I do not see that done either.
> > 
> > This is a first step (the tests are definitely going to fail if
> > they have incorrect information about the cache size).
> > 
> > For a fully reliable set of tests some major surgery will be required
> > to bind to CPUs and memory to control allocation and access.
> > 
> 
> What is the plan for making the tests more reliable? What is the
> use of this patch if it is just the first step?

Reinette,

I have no immediate plan to re-architect the the resctrl self-tests.
If you feel this step towards a solution is useless unless it is part
of a complete solution, then I can drop it from this series.

-Tony