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

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Message-ID: <0ceb405c-2f68-4aba-b146-333123e4d084@nvidia.com>
Date: Fri, 5 Dec 2025 13:51:16 -0800
From: Fenghua Yu <fenghuay@...dia.com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 Xiaochen Shen <shenxiaochen@...n-hieco.net>, tony.luck@...el.com,
 bp@...en8.de, shuah@...nel.org, skhan@...uxfoundation.org
Cc: babu.moger@....com, james.morse@....com, Dave.Martin@....com,
 x86@...nel.org, linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 3/3] selftests/resctrl: Fix non-contiguous CBM check
 for Hygon

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@...n-hieco.net>
>>> Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
>>> ---
>>> 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