linux-kernel - Re: [PATCH v3 01/10] x86/resctrl: Fix min_cbm

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Date:   Wed, 24 Aug 2022 10:58:15 -0500
From:   "Moger, Babu" <babu.moger@....com>
To:     Reinette Chatre <reinette.chatre@...el.com>, fenghua.yu@...el.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de
Cc:     eranian@...gle.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, corbet@....net, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, bagasdotme@...il.com
Subject: Re: [PATCH v3 01/10] x86/resctrl: Fix min_cbm_bits for AMD


On 8/23/22 15:56, Reinette Chatre wrote:
> Hi Babu,
>
> On 8/22/2022 6:42 AM, 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)
>>
>> 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%7Cd695c39eb7d94d659db008da8549ed74%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637968849807214070%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=prSwl8bTHx0y3o9hBNxp3u%2FNu8SrNcEWUwDOCQCVURk%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>
>> Reviewed-by: Ingo Molnar <mingo@...nel.org>
>> ---
>>  arch/x86/kernel/cpu/resctrl/core.c |    8 ++------
>>  1 file changed, 2 insertions(+), 6 deletions(-)
>>
>> 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;
>>
>>
> Thank you for putting this together.
>
> This change makes arch_has_empty_bitmaps redundant. Can it be removed?

Hi Reinette,

Actually, I thought about that. Sure. We can remove it.

-- 
Thanks
Babu Moger