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From:   "Moger, Babu" <Babu.Moger@amd.com>
To:     Reinette Chatre <reinette.chatre@intel.com>,
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        <pawan.kumar.gupta@linux.intel.com>,
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        "daniel.sneddon@linux.intel.com" <daniel.sneddon@linux.intel.com>,
        "Das1, Sandipan" <Sandipan.Das@amd.com>,
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        "james.morse@arm.com" <james.morse@arm.com>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "bagasdotme@gmail.com" <bagasdotme@gmail.com>,
        "eranian@google.com" <eranian@google.com>
Subject: RE: [PATCH v4 01/13] x86/resctrl: Fix min_cbm_bits for AMD
Thread-Topic: [PATCH v4 01/13] x86/resctrl: Fix min_cbm_bits for AMD
Thread-Index: AQHYwuOozRcLHsbJGU2Nw2onSO0Px63iQw0AgAAr7vA=
Date:   Fri, 16 Sep 2022 18:31:05 +0000
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References: <166257348081.1043018.11227924488792315932.stgit@bmoger-ubuntu>
 <166257359679.1043018.9253512972611409799.stgit@bmoger-ubuntu>
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[AMD Official Use Only - General]


> -----Original Message-----
> From: Reinette Chatre <reinette.chatre@intel.com>
> Sent: Friday, September 16, 2022 10:53 AM
> To: Moger, Babu <Babu.Moger@amd.com>; corbet@lwn.net;
> tglx@linutronix.de; mingo@redhat.com; bp@alien8.de
> Cc: fenghua.yu@intel.com; dave.hansen@linux.intel.com; x86@kernel.org;
> hpa@zytor.com; paulmck@kernel.org; akpm@linux-foundation.org;
> quic_neeraju@quicinc.com; rdunlap@infradead.org;
> damien.lemoal@opensource.wdc.com; songmuchun@bytedance.com;
> peterz@infradead.org; jpoimboe@kernel.org; pbonzini@redhat.com;
> chang.seok.bae@intel.com; pawan.kumar.gupta@linux.intel.com;
> jmattson@google.com; daniel.sneddon@linux.intel.com; Das1, Sandipan
> <Sandipan.Das@amd.com>; tony.luck@intel.com; james.morse@arm.com;
> linux-doc@vger.kernel.org; linux-kernel@vger.kernel.org;
> bagasdotme@gmail.com; eranian@google.com
> Subject: Re: [PATCH v4 01/13] x86/resctrl: Fix min_cbm_bits for AMD
>=20
> Hi Babu,
>=20
> On 9/7/2022 10:59 AM, Babu Moger wrote:
> > AMD systems support zero CBM (capacity bit mask) for L3 allocation.
>=20
> Above mentions "for L3 allocation", but the change impacts
> L3 as well as L2 allocation. Perhaps just "cache allocation"?
>=20
> > That is reflected in rdt_init_res_defs_amd() by:
> >
> > 	r->cache.arch_has_empty_bitmaps =3D true;
> >
> > However given the unified code in cbm_validate(), checking for:
> > 	val =3D=3D 0 && !arch_has_empty_bitmaps
> >
> > is not enough because of another check in cbm_validate():
> >
> > 	if ((zero_bit - first_bit) < r->cache.min_cbm_bits)
> >
> > The default value of r->cache.min_cbm_bits =3D 1.
> >
> > Leading to:
> >
> > 	$ cd /sys/fs/resctrl
> > 	$ mkdir foo
> > 	$ cd foo
> > 	$ echo L3:0=3D0 > schemata
> >           -bash: echo: write error: Invalid argument
> > 	$ cat /sys/fs/resctrl/info/last_cmd_status
> > 	  Need at least 1 bits in the mask
> >
> > Fix the issue by initializing the min_cbm_bits to 0 for AMD. Also,
> > remove the default setting of min_cbm_bits and initialize it separately=
.
> >
> > After the fix
> > 	$ cd /sys/fs/resctrl
> > 	$ mkdir foo
> > 	$ cd foo
> > 	$ echo L3:0=3D0 > schemata
> > 	$ cat /sys/fs/resctrl/info/last_cmd_status
> > 	  ok
> >
> > Link:
> > https://nam11.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Flor=
e
> > .kernel.org%2Flkml%2F20220517001234.3137157-1-
> eranian%40google.com%2F&
> >
> amp;data=3D05%7C01%7Cbabu.moger%40amd.com%7Cfdccc20e6a234fb3872a0
> 8da97fb
> >
> 94fc%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C6379894040498
> 44076%7
> >
> CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI
> 6Ik1
> >
> haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=3DDIpkBAkI7lAjj5QQ4
> 5VahssT
> > dWGj%2FcUwGJDiHXNYzz8%3D&amp;reserved=3D0
> > Fixes: 316e7f901f5a ("x86/resctrl: Add struct
> > rdt_cache::arch_has_{sparse, empty}_bitmaps")
> > Signed-off-by: Stephane Eranian <eranian@google.com>
> > Signed-off-by: Babu Moger <babu.moger@amd.com>
> > Reviewed-by: Ingo Molnar <mingo@kernel.org>
>=20
> (apart from the changelog nitpick)
>=20
> Thank you for clarifying the way forward for this fix.
>=20
> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>

Thank you
Babu Moger