linux-kernel - RE: resctrl2

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Message-ID: <SJ1PR11MB6083849D1AEF44806C4D669AFCEDA@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date:   Fri, 8 Sep 2023 18:51:03 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     "babu.moger@....com" <babu.moger@....com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "james.morse@....com" <james.morse@....com>
CC:     Amit Singh Tomar <amitsinght@...vell.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        George Cherian <gcherian@...vell.com>,
        "robh@...nel.org" <robh@...nel.org>,
        "peternewman@...gle.com" <peternewman@...gle.com>,
        Drew Fustini <dfustini@...libre.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: resctrl2 - status

> > Can you try this out on an AMD system. I think I covered most of the
> > existing AMD resctrl features, but I have no machine to test the code
> > on, so very likely there are bugs in these code paths.
> >
> > I'd like to make any needed changes now, before I start breaking this
> > into reviewable bite-sized patches to avoid too much churn.
>
> I tried your latest code briefly on my system.  Unfortunately, I could
> not get it to work on my AMD system.
>
> # git branch -a
>    next
> * resctrl2_v65
> # ]# uname -r
> 6.5.0+
> #lsmod |grep rdt
> rdt_show_ids           12288  0
> rdt_mbm_local_bytes    12288  0
> rdt_mbm_total_bytes    12288  0
> rdt_llc_occupancy      12288  0
> rdt_l3_cat             16384  0
>
> # lsmod |grep mbe
> amd_mbec               16384  0
>
> I could not get  rdt_l3_mba
>
> # modprobe rdt_l3_mba
> modprobe: ERROR: could not insert 'rdt_l3_mba': No such device
>
> I don't see any data for the default group either.
>
> mount  -t resctrl resctrl /sys/fs/resctrl/
>
> cd /sys/fs/resctrl/mon_data/mon_L3_00
>
> cat mbm_summary
>       n/a      n/a /

Babu,

Thank a bunch for taking this for a quick spin. There's several bits of
good news there. Several modules automatically loaded as expected.
Nothing went "OOPS" and crashed the system.

Here’s the code that the rdt_l3_mba module runs that can cause failure
to load with "No such device"

        if (!boot_cpu_has(X86_FEATURE_RDT_A)) {
                pr_debug("No RDT allocation support\n");
                return -ENODEV;
        }

        mba_features = cpuid_ebx(0x10);

        if (!(mba_features & BIT(3))) {
                pr_debug("No RDT MBA allocation\n");
                return -ENODEV;
        }

I assume the first test must have succeeded (same code in rdt_l3_cat, and
that loaded OK). So must be the second. How does AMD enumerate MBA
support?

Less obvious what is the root cause of the mbm_summary file to fail to
show any data. rdt_mbm_local_bytes  and rdt_mbm_total_bytes  modules
loaded OK. So I'm looking for the right CPUID bits to detect memory bandwidth
monitoring.

-Tony