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SubjectRE: [PATCH V1 01/13] selftests/resctrl: Fix feature detection
Date
Hi Reinette,

> -----Original Message-----
> From: Reinette Chatre <reinette.chatre@intel.com>
> Sent: Monday, March 9, 2020 2:45 PM
> To: Prakhya, Sai Praneeth <sai.praneeth.prakhya@intel.com>;
> shuah@kernel.org; linux-kselftest@vger.kernel.org
> Cc: tglx@linutronix.de; mingo@redhat.com; bp@alien8.de; Luck, Tony
> <tony.luck@intel.com>; babu.moger@amd.com; james.morse@arm.com;
> Shankar, Ravi V <ravi.v.shankar@intel.com>; Yu, Fenghua
> <fenghua.yu@intel.com>; x86@kernel.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH V1 01/13] selftests/resctrl: Fix feature detection
>
> Hi Sai,
>
> On 3/6/2020 7:40 PM, Sai Praneeth Prakhya wrote:
> > From: Reinette Chatre <reinette.chatre@intel.com>
> >
> > The intention of the resctrl selftests is to only run the tests
> > associated with the feature(s) supported by the platform. Through
> > parsing of the feature flags found in /proc/cpuinfo it is possible to
> > learn which features are supported by the plaform.
> >
> > There are currently two issues with the platform feature detection
> > that together result in tests always being run, whether the platform
> > supports a feature or not. First, the parsing of the the feature flags
> > loads the line containing the flags in a buffer that is too small (256
> > bytes) to always contain all flags. The consequence is that the flags
> > of the features being tested for may not be present in the buffer.
> > Second, the actual test for presence of a feature has an error in the
> > logic, negating the test for a particular feature flag instead of
> > testing for the presence of a particular feature flag.
> >
> > These two issues combined results in all tests being run on all
> > platforms, whether the feature is supported or not.
> >
> > Fix these issue by (1) increasing the buffer size being used to parse
> > the feature flags, and (2) change the logic to test for presence of
> > the feature being tested for.
> >
> > Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> > Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> > ---
> > tools/testing/selftests/resctrl/resctrlfs.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/testing/selftests/resctrl/resctrlfs.c
> > b/tools/testing/selftests/resctrl/resctrlfs.c
> > index 19c0ec4045a4..226dd7fdcfb1 100644
> > --- a/tools/testing/selftests/resctrl/resctrlfs.c
> > +++ b/tools/testing/selftests/resctrl/resctrlfs.c
> > @@ -596,11 +596,11 @@ bool check_resctrlfs_support(void)
> >
> > char *fgrep(FILE *inf, const char *str) {
> > - char line[256];
> > int slen = strlen(str);
> > + char line[2048];
> >
> > while (!feof(inf)) {
> > - if (!fgets(line, 256, inf))
> > + if (!fgets(line, 2048, inf))
> > break;
> > if (strncmp(line, str, slen))
> > continue;
> > @@ -631,7 +631,7 @@ bool validate_resctrl_feature_request(char
> *resctrl_val)
> > if (res) {
> > char *s = strchr(res, ':');
> >
> > - found = s && !strstr(s, resctrl_val);
> > + found = s && strstr(s, resctrl_val);
> > free(res);
> > }
> > fclose(inf);
> >
>
> Please note that this is only a partial fix. The current feature detection relies on
> the feature flags found in /proc/cpuinfo. Quirks and kernel boot parameters are
> not taken into account. This fix only addresses the parsing of feature flags. If a
> feature has been disabled via kernel boot parameter or quirk then the resctrl
> tests would still attempt to run the test for it.

That's a good point and makes sense to me. I think we could fix it in two ways
1. grep for strings in dmesg but that will still leave ambiguity in deciding b/w mbm and cqm because kernel prints "resctrl: L3 monitoring detected" for both the features
2. Check in "info" directory
a. For cat_l3, we could search for info/L3
b. For mba, we could search for info/MB
c. For cqm and mbm, we could search for specified string in info/L3_MON/mon_features

I think option 2 might be better because it can handle all cases, please let me know what you think.

Regards,
Sai
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