Re: [PATCH v2 3/3] selftests/resctrl: Fix non-contiguous CBM check for Hygon

[Fenghua Yu]

Hi, Reinette,

On 12/5/25 13:30, Reinette Chatre wrote:
> Hi Fenghua,
>
> On 12/5/25 11:39 AM, Fenghua Yu wrote:
> > On 12/5/25 01:25, Xiaochen Shen wrote:
> > > The resctrl selftest currently fails on Hygon CPUs that always supports
> > > non-contiguous CBM, printing the error:
> > >
> > >     "# Hardware and kernel differ on non-contiguous CBM support!"
> > >
> > > This occurs because the arch_supports_noncont_cat() function lacks
> > > vendor detection for Hygon CPUs, preventing proper identification of
> > > their non-contiguous CBM capability.
> > >
> > > Fix this by adding Hygon vendor ID detection to
> > > arch_supports_noncont_cat().
> > >
> > > Signed-off-by: Xiaochen Shen <shenxiaochen@xxxxxxxxxxxxxx>
> > > Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> > > ---
> > > Maintainer note:
> > > Even though this is a fix it is not a candidate for backport since it is
> > > based on another patch series (x86/resctrl: Fix Platform QoS issues for
> > > Hygon) which is in process of being added to resctrl.
> > >
> > >    tools/testing/selftests/resctrl/cat_test.c | 4 ++--
> > >    1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
> > > index 94cfdba5308d..59a0f80fdc5a 100644
> > > --- a/tools/testing/selftests/resctrl/cat_test.c
> > > +++ b/tools/testing/selftests/resctrl/cat_test.c
> > > @@ -290,8 +290,8 @@ static int cat_run_test(const struct resctrl_test *test, const struct user_param
> > >      static bool arch_supports_noncont_cat(const struct resctrl_test *test)
> > >    {
> > > -    /* AMD always supports non-contiguous CBM. */
> > > -    if (get_vendor() == ARCH_AMD)
> > > +    /* AMD and Hygon always supports non-contiguous CBM. */
> > > +    if (get_vendor() == ARCH_AMD || get_vendor() == ARCH_HYGON)
> >
> > nit. Better to avoid call get_vendor() twice (or even more in the future)?
>
> Are you perhaps referring to detect_vendor()? detect_vendor() does the actual digging to
> determine the vendor ID and is indeed called just once by get_vendor(). In subsequent calls
> get_vendor() just returns the static ID.

There is still cost to call get_vendor() (call, push, cmp, pop, ret, 
etc) in subsequent calls. I just feel it's redundant to call it multiple 
times in just one sentence.

Thanks.

-Fenghua