Messages in this thread | | | Subject | Re: [PATCH] ACPI/HMAT: Fix the parsing of Cache Associativity and Write Policy | From | Tao Xu <> | Date | Tue, 10 Dec 2019 21:18:47 +0800 |
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On 12/10/2019 4:27 PM, Rafael J. Wysocki wrote: > On Tue, Dec 10, 2019 at 9:19 AM Tao Xu <tao3.xu@intel.com> wrote: >> >> On 12/10/2019 4:06 PM, Rafael J. Wysocki wrote: >>> On Tue, Dec 10, 2019 at 2:04 AM Tao Xu <tao3.xu@intel.com> wrote: >>>> >>>> On 12/9/2019 6:01 PM, Rafael J. Wysocki wrote: >>>>> On Mon, Dec 2, 2019 at 8:03 AM Tao Xu <tao3.xu@intel.com> wrote: >>>>>> >>>>>> In chapter 5.2.27.5, Table 5-147: Field "Cache Attributes" of >>>>>> ACPI 6.3 spec: 0 is "None", 1 is "Direct Mapped", 2 is "Complex Cache >>>>>> Indexing" for Cache Associativity; 0 is "None", 1 is "Write Back", >>>>>> 2 is "Write Through" for Write Policy. >>>>> >>>>> Well, I'm not sure what the connection between the above statement, >>>>> which is correct AFAICS, and the changes made by the patch is. >>>>> >>>>> Is that the *_OTHER symbol names are confusing or something deeper? >>>>> >>>> >>>> Because in include/acpi/actbl1.h: >>>> >>>> #define ACPI_HMAT_CA_NONE (0) >>>> >>>> ACPI_HMAT_CA_NONE is 0, but in include/linux/node.h: >>>> >>>> enum cache_indexing { >>>> NODE_CACHE_DIRECT_MAP, >>>> NODE_CACHE_INDEXED, >>>> NODE_CACHE_OTHER, >>>> }; >>>> NODE_CACHE_OTHER is 2, and for otner enum: >>>> >>>> case ACPI_HMAT_CA_DIRECT_MAPPED: >>>> tcache->cache_attrs.indexing = NODE_CACHE_DIRECT_MAP; >>>> break; >>>> case ACPI_HMAT_CA_COMPLEX_CACHE_INDEXING: >>>> tcache->cache_attrs.indexing = NODE_CACHE_INDEXED; >>>> break; >>>> in include/acpi/actbl1.h: >>>> >>>> #define ACPI_HMAT_CA_DIRECT_MAPPED (1) >>>> #define ACPI_HMAT_CA_COMPLEX_CACHE_INDEXING (2) >>>> >>>> but in include/linux/node.h: >>>> >>>> NODE_CACHE_DIRECT_MAP is 0, NODE_CACHE_INDEXED is 1. This is incorrect. >>> >>> Why is it incorrect? >> >> Sorry I paste the wrong pre-define. >> >> This is the incorrect line: >> >> case ACPI_HMAT_CA_DIRECT_MAPPED: >> tcache->cache_attrs.indexing = NODE_CACHE_DIRECT_MAP; >> >> ACPI_HMAT_CA_DIRECT_MAPPED is 1, NODE_CACHE_DIRECT_MAP is 0. That means >> if HMAT table input 1 for cache_attrs.indexing, kernel store 0 in >> cache_attrs.indexing. But in ACPI 6.3, 0 means "None". So for the whole >> switch codes: > > This is a mapping between the ACPI-defined values and the generic ones > defined in the kernel. There is not rule I know of by which they must > be the same numbers. Or is there such a rule which I'm missing? > > As long as cache_attrs.indexing is used consistently going forward, > the difference between the ACPI-defined numbers and its values > shouldn't matter, should it? > Yes, it will not influence the ACPI HMAT tables. Only influence is the sysfs, as in https://www.kernel.org/doc/html/latest/admin-guide/mm/numaperf.html:
# tree sys/devices/system/node/node0/memory_side_cache/ /sys/devices/system/node/node0/memory_side_cache/ |-- index1 | |-- indexing | |-- line_size | |-- size | `-- write_policy
indexing is parsed in this file, so it can be read by user-space. Although now there is no user-space tool use this information to do some thing. But I am wondering if it is used in the future, someone use it to show the memory side cache information to user or use it to do performance turning.
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