Re: [PATCH] ACPI/HMAT: Fix the parsing of Cache Associativity and Write Policy

[Tao Xu]

On 12/10/19 9:18 PM, Tao Xu wrote:
> On 12/10/2019 4:27 PM, Rafael J. Wysocki wrote:
> > On Tue, Dec 10, 2019 at 9:19 AM Tao Xu <tao3.xu@xxxxxxxxx> 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@xxxxxxxxx> 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@xxxxxxxxx> 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_NONEÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ (0)
> > > > >
> > > > > ACPI_HMAT_CA_NONE is 0, but in include/linux/node.h:
> > > > >
> > > > > ÂÂÂÂÂ enum cache_indexing {
> > > > > ÂÂÂÂÂÂÂÂÂÂÂÂ NODE_CACHE_DIRECT_MAP,
> > > > > ÂÂÂÂÂÂÂÂÂÂÂÂ NODE_CACHE_INDEXED,
> > > > > ÂÂÂÂÂÂÂÂÂÂÂÂ NODE_CACHE_OTHER,
> > > > > ÂÂÂÂÂ };
> > > > > NODE_CACHE_OTHER is 2, and for otner enum:
> > > > >
> > > > > ÂÂÂÂÂÂÂÂÂÂÂ case ACPI_HMAT_CA_DIRECT_MAPPED:
> > > > > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ tcache->cache_attrs.indexing = 
> > > > > NODE_CACHE_DIRECT_MAP;
> > > > > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ break;
> > > > > ÂÂÂÂÂÂÂÂÂÂÂ case ACPI_HMAT_CA_COMPLEX_CACHE_INDEXING:
> > > > > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ tcache->cache_attrs.indexing = NODE_CACHE_INDEXED;
> > > > > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ break;
> > > > > in include/acpi/actbl1.h:
> > > > >
> > > > > ÂÂÂ #define ACPI_HMAT_CA_DIRECT_MAPPEDÂÂÂÂÂÂÂÂÂÂÂ (1)
> > > > > ÂÂÂ #define ACPI_HMAT_CA_COMPLEX_CACHE_INDEXINGÂÂ (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
> |ÂÂ |-- indexing
> |ÂÂ |-- line_size
> |ÂÂ |-- size
> |ÂÂ `-- 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.

I finish a test using emulated ACPI HMAT from QEMU
(branch:hmat https://github.com/taoxu916/qemu.git)

And I get the kernel log and sysfs output:
[    0.954288] HMAT: Cache: Domain:0 Size:20480 Attrs:00081111 SMBIOS 
Handles:0
[    0.954835] HMAT: Cache: Domain:1 Size:15360 Attrs:00081111 SMBIOS 
Handles:0

/sys/devices/system/node/node0/memory_side_cache/index1 # cat indexing
0
/sys/devices/system/node/node0/memory_side_cache/index1 # cat write_policy
0

Note that 'Attrs' is printed using %x, so we can get:
(attrs & ACPI_HMAT_CACHE_ASSOCIATIVITY) >> 8 = 1,
(attrs & ACPI_HMAT_WRITE_POLICY) >> 12       = 1

but we get 0 in sysfs, so if user or software read this information and 
read the ACPI 6.3 spec, will think there is 'none' for Cache 
Associativity or Write Policy.

p.s. the qemu input CLI:

./x86_64-softmmu/qemu-system-x86_64 \
-machine pc,hmat=on -nographic \
-kernel ./bzImage \
-initrd ./initramfs-virt \
-append console=ttyS0 \
-m 2G \
-smp 2,sockets=2 \
-object memory-backend-ram,size=1G,id=m0 \
-object memory-backend-ram,size=1G,id=m1 \
-numa node,nodeid=0,memdev=m0 \
-numa node,nodeid=1,memdev=m1,initiator=0 \
-numa cpu,node-id=0,socket-id=0 \
-numa cpu,node-id=0,socket-id=1 \
-numa 
hmat-lb,initiator=0,target=0,hierarchy=memory,data-type=access-latency,latency=20 
\
-numa 
hmat-lb,initiator=0,target=0,hierarchy=memory,data-type=access-bandwidth,bandwidth=200M 
\
-numa 
hmat-lb,initiator=0,target=1,hierarchy=memory,data-type=access-latency,latency=65 
\
-numa 
hmat-lb,initiator=0,target=1,hierarchy=memory,data-type=access-bandwidth,bandwidth=200M 
\
-numa 
hmat-cache,node-id=0,size=20K,level=1,associativity=direct,policy=write-back,line=8 
\
-numa 
hmat-cache,node-id=1,size=15K,level=1,associativity=direct,policy=write-back,line=8