linux-kernel - Re: [PATCH v4 01/13] x86/resctrl: Fix min_cbm

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Date:   Mon, 12 Sep 2022 09:54:23 -0500
From:   "Moger, Babu" <babu.moger@....com>
To:     James Morse <james.morse@....com>, corbet@....net,
        reinette.chatre@...el.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de
Cc:     fenghua.yu@...el.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, paulmck@...nel.org, akpm@...ux-foundation.org,
        quic_neeraju@...cinc.com, rdunlap@...radead.org,
        damien.lemoal@...nsource.wdc.com, songmuchun@...edance.com,
        peterz@...radead.org, jpoimboe@...nel.org, pbonzini@...hat.com,
        chang.seok.bae@...el.com, pawan.kumar.gupta@...ux.intel.com,
        jmattson@...gle.com, daniel.sneddon@...ux.intel.com,
        sandipan.das@....com, tony.luck@...el.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        bagasdotme@...il.com, eranian@...gle.com
Subject: Re: [PATCH v4 01/13] x86/resctrl: Fix min_cbm_bits for AMD

Hi James,

On 9/9/22 12:00, James Morse wrote:
> Hi Babu,
>
> On 07/09/2022 18:59, Babu Moger wrote:
>> AMD systems support zero CBM (capacity bit mask) for L3 allocation.
>> That is reflected in rdt_init_res_defs_amd() by:
>>
>> 	r->cache.arch_has_empty_bitmaps = true;
>>
>> However given the unified code in cbm_validate(), checking for:
>> 	val == 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)
> Right, the Intel version had this, but the AMD didn't. I evidently only thought about this
> the !arch_has_empty_bitmaps way round! Sorry about that.

>
>
>> The default value of r->cache.min_cbm_bits = 1.
>>
>> Leading to:
>>
>> 	$ cd /sys/fs/resctrl
>> 	$ mkdir foo
>> 	$ cd foo
>> 	$ echo L3:0=0 > 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=0 > schemata
>> 	$ cat /sys/fs/resctrl/info/last_cmd_status
>> 	  ok
>>
>> Link: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2F20220517001234.3137157-1-eranian%40google.com%2F&amp;data=05%7C01%7Cbabu.moger%40amd.com%7Cc5b955e9726344c550f008da9284dedd%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637983396695085653%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=wIVM5%2BrCwfWDpIrLkDtycgoCd4PWMC3D8y%2FAjshIW%2FQ%3D&amp;reserved=0
>> Fixes: 316e7f901f5a ("x86/resctrl: Add struct rdt_cache::arch_has_{sparse, empty}_bitmaps")
>> Signed-off-by: Stephane Eranian <eranian@...gle.com>
>> Signed-off-by: Babu Moger <babu.moger@....com>
> Er, who is the author if this patch? If you are reposting Stephane's patch then there
> needs to be a 'From: ' at the top of the email so that git preserves the ownership. You

I can add Stephane's name in "From" if it is right thing to do. But this
patch was modified from the original version Stephane posted.

https://lore.kernel.org/lkml/20220517001234.3137157-1-eranian@google.com/


> may need some incantation of "git commit --amend --author=" to fix this in your tree.
>
> As its a fix, have you posted this separately? Mixing fixes and new-code makes it hard for
> the maintainer to spot what needs to be taken for the next -rc.

ok. I can send this separate in next version.


>
>
>> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
>> index bb1c3f5f60c8..a5c51a14fbce 100644
>> --- a/arch/x86/kernel/cpu/resctrl/core.c
>> +++ b/arch/x86/kernel/cpu/resctrl/core.c
>> @@ -66,9 +66,6 @@ struct rdt_hw_resource rdt_resources_all[] = {
>>  			.rid			= RDT_RESOURCE_L3,
>>  			.name			= "L3",
>>  			.cache_level		= 3,
>> -			.cache = {
>> -				.min_cbm_bits	= 1,
>> -			},
>>  			.domains		= domain_init(RDT_RESOURCE_L3),
>>  			.parse_ctrlval		= parse_cbm,
>>  			.format_str		= "%d=%0*x",
>> @@ -83,9 +80,6 @@ struct rdt_hw_resource rdt_resources_all[] = {
>>  			.rid			= RDT_RESOURCE_L2,
>>  			.name			= "L2",
>>  			.cache_level		= 2,
>> -			.cache = {
>> -				.min_cbm_bits	= 1,
>> -			},
>>  			.domains		= domain_init(RDT_RESOURCE_L2),
>>  			.parse_ctrlval		= parse_cbm,
>>  			.format_str		= "%d=%0*x",
>> @@ -877,6 +871,7 @@ static __init void rdt_init_res_defs_intel(void)
>>  			r->cache.arch_has_sparse_bitmaps = false;
>>  			r->cache.arch_has_empty_bitmaps = false;
>>  			r->cache.arch_has_per_cpu_cfg = false;
>> +			r->cache.min_cbm_bits = 1;
>>  		} else if (r->rid == RDT_RESOURCE_MBA) {
>>  			hw_res->msr_base = MSR_IA32_MBA_THRTL_BASE;
>>  			hw_res->msr_update = mba_wrmsr_intel;
>> @@ -897,6 +892,7 @@ static __init void rdt_init_res_defs_amd(void)
>>  			r->cache.arch_has_sparse_bitmaps = true;
>>  			r->cache.arch_has_empty_bitmaps = true;
>>  			r->cache.arch_has_per_cpu_cfg = true;
>> +			r->cache.min_cbm_bits = 0;
>>  		} else if (r->rid == RDT_RESOURCE_MBA) {
>>  			hw_res->msr_base = MSR_IA32_MBA_BW_BASE;
>>  			hw_res->msr_update = mba_wrmsr_amd;
>>
>>
>
> Reviewed-by: James Morse <james.morse@....com>


Thank You.

Babu