[RFC v2 7/7] qemu-options: Add the cache topology description of -smp

Zhao Liu
2024-05-30T10:01:03Z

Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
Changes since RFC v1:
* Use "*_cache=topo_level" as -smp example as the original "level"
term for a cache has a totally different meaning. (Jonathan)
---
qemu-options.hx | 50 +++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 44 insertions(+), 6 deletions(-)

diff --git a/qemu-options.hx b/qemu-options.hx
index 8ca7f34ef0c8..29d8a4b9b68b 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -282,7 +282,8 @@ ERST
DEF("smp", HAS_ARG, QEMU_OPTION_smp,
"-smp [[cpus=]n][,maxcpus=maxcpus][,drawers=drawers][,books=books][,sockets=sockets]\n"
" [,dies=dies][,clusters=clusters][,modules=modules][,cores=cores]\n"
- " [,threads=threads]\n"
+ " [,threads=threads][,l1d-cache=topo_level][,l1i-cache=topo_level]\n"
+ " [,l2-cache=topo_level][,l3-cache=topo_level]\n"
" set the number of initial CPUs to 'n' [default=1]\n"
" maxcpus= maximum number of total CPUs, including\n"
" offline CPUs for hotplug, etc\n"
@@ -294,7 +295,11 @@ DEF("smp", HAS_ARG, QEMU_OPTION_smp,
" modules= number of modules in one cluster\n"
" cores= number of cores in one module\n"
" threads= number of threads in one core\n"
- "Note: Different machines may have different subsets of the CPU topology\n"
+ " l1d-cache= topology level of L1 D-cache\n"
+ " l1i-cache= topology level of L1 I-cache\n"
+ " l2-cache= topology level of L2 cache\n"
+ " l3-cache= topology level of L3 cache\n"
+ "Note: Different machines may have different subsets of the CPU and cache topology\n"
" parameters supported, so the actual meaning of the supported parameters\n"
" will vary accordingly. For example, for a machine type that supports a\n"
" three-level CPU hierarchy of sockets/cores/threads, the parameters will\n"
@@ -308,7 +313,7 @@ DEF("smp", HAS_ARG, QEMU_OPTION_smp,
" must be set as 1 in the purpose of correct parsing.\n",
QEMU_ARCH_ALL)
SRST
-``-smp [[cpus=]n][,maxcpus=maxcpus][,drawers=drawers][,books=books][,sockets=sockets][,dies=dies][,clusters=clusters][,modules=modules][,cores=cores][,threads=threads]``
+``-smp [[cpus=]n][,maxcpus=maxcpus][,drawers=drawers][,books=books][,sockets=sockets][,dies=dies][,clusters=clusters][,modules=modules][,cores=cores][,threads=threads][,l1d-cache=topo_level][,l1i-cache=topo_level][,l2-cache=topo_level][,l3-cache=topo_level]``
Simulate a SMP system with '\ ``n``\ ' CPUs initially present on
the machine type board. On boards supporting CPU hotplug, the optional
'\ ``maxcpus``\ ' parameter can be set to enable further CPUs to be
@@ -322,15 +327,34 @@ SRST
Both parameters are subject to an upper limit that is determined by
the specific machine type chosen.

+ CPU topology parameters include '\ ``drawers``\ ', '\ ``books``\ ',
+ '\ ``sockets``\ ', '\ ``dies``\ ', '\ ``clusters``\ ', '\ ``modules``\ ',
+ '\ ``cores``\ ' and '\ ``threads``\ '. These CPU parameters accept only
+ integers and are used to specify the number of specific topology domains
+ under the corresponding topology level.
+
To control reporting of CPU topology information, values of the topology
parameters can be specified. Machines may only support a subset of the
- parameters and different machines may have different subsets supported
- which vary depending on capacity of the corresponding CPU targets. So
- for a particular machine type board, an expected topology hierarchy can
+ CPU topology parameters and different machines may have different subsets
+ supported which vary depending on capacity of the corresponding CPU targets.
+ So for a particular machine type board, an expected topology hierarchy can
be defined through the supported sub-option. Unsupported parameters can
also be provided in addition to the sub-option, but their values must be
set as 1 in the purpose of correct parsing.

+ Cache topology parameters include '\ ``l1d-cache``\ ', '\ ``l1i-cache``\ ',
+ '\ ``l2-cache``\ ' and '\ ``l3-cache``\ '. These cache topology parameters
+ accept the strings of CPU topology levels (such as '\ ``drawer``\ ', '\ ``book``\ ',
+ '\ ``socket``\ ', '\ ``die``\ ', '\ ``cluster``\ ', '\ ``module``\ ',
+ '\ ``core``\ ' or '\ ``thread``\ '). Exactly which topology level strings
+ could be accepted as the parameter depends on the machine's support for the
+ corresponding CPU topology level.
+
+ Machines may also only support a subset of the cache topology parameters.
+ Unsupported cache topology parameters will be omitted, and correspondingly,
+ the target CPU's cache topology will use the its default cache topology
+ setting.
+
Either the initial CPU count, or at least one of the topology parameters
must be specified. The specified parameters must be greater than zero,
explicit configuration like "cpus=0" is not allowed. Values for any
@@ -356,6 +380,20 @@ SRST

-smp 32,sockets=2,dies=2,modules=2,cores=2,threads=2,maxcpus=32

+ The following sub-option defines a CPU topology hierarchy (2 sockets
+ totally on the machine, 2 dies per socket, 2 modules per die, 2 cores per
+ module, 2 threads per core) with 3-level cache topology hierarchy (L1
+ D-cache per core, L1 I-cache per core, L2 cache per core and L3 cache per
+ die) for PC machines which support sockets/dies/modules/cores/threads.
+ Some members of the CPU topology option can be omitted but their values
+ will be automatically computed. Some members of the cache topology
+ option can also be omitted and target CPU will use the default topology.:
+
+ ::
+
+ -smp 32,sockets=2,dies=2,modules=2,cores=2,threads=2,maxcpus=32,\
+ l1d-cache=core,l1i-cache=core,l2-cache=core,l3-cache=die
+
The following sub-option defines a CPU topology hierarchy (2 sockets
totally on the machine, 2 clusters per socket, 2 cores per cluster,
2 threads per core) for ARM virt machines which support sockets/clusters
--
2.34.1