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Re: [PATCH v2 3/8] machine: Print supported CPU models instead of typena
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From: |
Gavin Shan |
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Subject: |
Re: [PATCH v2 3/8] machine: Print supported CPU models instead of typenames |
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Date: |
Tue, 29 Aug 2023 16:28:45 +1000 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 |
Hi Igor,
On 8/29/23 00:46, Igor Mammedov wrote:
On Mon, 31 Jul 2023 15:07:30 +1000
Gavin Shan <gshan@redhat.com> wrote:
On 7/27/23 19:00, Igor Mammedov wrote:
On Thu, 27 Jul 2023 15:16:18 +1000
Gavin Shan <gshan@redhat.com> wrote:
On 7/27/23 09:08, Richard Henderson wrote:
On 7/25/23 17:32, Gavin Shan wrote:
-static const char *q800_machine_valid_cpu_types[] = {
+static const char * const q800_machine_valid_cpu_types[] = {
M68K_CPU_TYPE_NAME("m68040"),
NULL
};
+static const char * const q800_machine_valid_cpu_models[] = {
+ "m68040",
+ NULL
+};
I really don't like this replication.
Right, it's going to be lots of replications, but gives much flexibility.
There are 21 targets and we don't have fixed pattern for the mapping between
CPU model name and CPU typename. I'm summarizing the used patterns like below.
1 All CPU model names are mappinged to fixed CPU typename;
plainly spelled it would be: cpu_model name ignored and
a cpu type is returned anyways.
I'd make this hard error right away, as "junk in => error out"
it's clearly user error. I think we don't even have to follow
deprecation process for that.
Right, It's not expected behavior to map ambiguous CPU model names to
the fixed CPU typename.
to be nice we can deprecate those and then later remove.
(while deprecating make those targets accept typenames)
Lets put it aside for now and revisit it later, so that we can focus on
the conversion from the CPU type name to the CPU model name for now.
2 CPU model name is same to CPU typename;
3 CPU model name is alias to CPU typename;
4 CPU model name is prefix of CPU typename;
and some more:
5. cpu model names aren't names at all sometimes, and some other
CPU property is used. (ppc)
This one I'd prefer to get rid of and ppc handling more consistent
with other targets, which would need PPC folks to persuaded to drop
PVR lookup.
I put this into class 3, meaning the PVRs are regarded as aliases to CPU
typenames.
with PPC using 'true' aliases, -cpu input is lost after it's translated into
typename.
(same for alpha)
it also adds an extra fun with 'max' cpu model but that boils down to above
statement.
(same for
* sh4
* cris(in user mode only, but you are making sysemu extension, so it doesn't
count)
)
For this class of aliases reverse translation won't yield the same
result as used -cpu. The only option you have is to store -cpu cpu_model
somewhere (use qemu_opts??, and then fetch it later to print in error message)
x86 has 'aliases' as well, but in reality it creates distinct cpu types
for each 'alias', so it's possible to do reverse translation.
It's true that '-cpu input' gets lost in these cases. However, the CPU type
name instead of the CPU model name is printed in the error message when the
CPU type is validated in hw/core/machine.c::machine_run_board_init(). It looks
good to me to print the CPU type name instead of the model name there.
Another error message is printed when the CPU model specified in '-cpu input'
isn't valid. The CPU model has been printed and it looks good either.
# qemu-system-aarch64 -M virt -cpu aaa
qemu-system-aarch64: unable to find CPU model 'aaa'
Are there other cases I missed where we need to print the CPU model name, which
is specified by user through '-cpu input'?
Target Categories suffix-of-CPU-typename
-------------------------------------------------------
alpha -234 -alpha-cpu
arm ---4 -arm-cpu
avr -2--
cris --34 -cris-cpu
hexagon ---4 -hexagon-cpu
hppa 1---
i386 ---4 -i386-cpu
loongarch -2-4 -loongarch-cpu
m68k ---4 -m68k-cpu
microblaze 1---
mips ---4 -mips64-cpu -mips-cpu
nios2 1---
openrisc ---4 -or1k-cpu
ppc --34 -powerpc64-cpu -powerpc-cpu
riscv ---4 -riscv-cpu
rx -2-4 -rx-cpu
s390x ---4 -s390x-cpu
sh4 --34 -superh-cpu
sparc -2--
it's case 4
Yes.
tricore ---4 -tricore-cpu
xtensa ---4 -xtensa-cpu
There are several options as below. Please let me know which one or something
else is the best.
(a) Keep what we have and use mc->valid_{cpu_types, cpu_models}[] to track
the valid CPU typenames and CPU model names.
(b) Introduce CPUClass::model_name_by_typename(). Every target has their own
implementation to convert CPU typename to CPU model name. The CPU model name
is parsed from mc->valid_cpu_types[i].
char *CPUClass::model_by_typename(const char *typename);
(c) As we discussed before, use mc->valid_cpu_type_suffix and
mc->valid_cpu_models
because the CPU type check is currently needed by target arm/m68k/riscv where we
do have fixed pattern to convert CPU model names to CPU typenames. The CPU
typename
is comprised of CPU model name and suffix. However, it won't be working when
the CPU
type check is required by other target where we have patterns other than this.
none of above is really good, that's why I was objecting to introducing
reverse type->name mapping. That ends up with increased amount junk,
and it's not because your patches are bad, but because you are trying
to deal with cpu model names (which is a historically evolved mess).
The best from engineering POV would be replacing CPU models with
type names.
Even though it's a bit radical, I very much prefer replacing
cpu_model names with '-cpu type'usage directly. Making it
consistent with -device/other interfaces and coincidentally that
obsoletes need in reverse name mapping.
It's painful for end users who will need to change configs/scripts,
but it's one time job. Additionally from QEMU pov, codebase
will be less messy => more maintainable which benefits not only
developers but end-users in the end.
I have to clarify the type->model mapping has been existing since the
model->type mapping was introduced with the help of CPU_RESOLVING_TYPE.
I mean the logic has been existing since the existence of CPU_RESOLVING_TYPE,
even the code wasn't there.
I'm not sure about the idea to switch to '-cpu <cpu-type-name>' since
it was rejected by Peter Maydell before. Hope Peter can double confirm
for this. For me, the shorter name is beneficial. For example, users
needn't to have '-cpu host-arm-cpu' for '-cpu host'.
[rant:
It's the same story repeating over and over, when it comes to
changing QEMU CLI, which hits resistance wall. But with QEMU
deprecation process we've changed CLI behavior before,
despite of that world didn't cease to exist and users
have adapted to new QEMU and arguably QEMU became a tiny
bit more maintainable since we don't have to deal some
legacy behavior.
]
I need more context about 'deprecation process' here. My understanding
is both CPU typename and model name will be accepted for a fixed period
of time. However, a warning message will be given to indicate that the
model name will be obsoleted soon. Eventually, we switch to CPU typename
completely. Please correct me if there are anything wrong.
yep, that's the gist of deprecation in this case.
Ok. Thanks for your confirm.
Another idea back in the days was (as a compromise),
1. keep using keep valid_cpu_types
2. instead of introducing yet another way to do reverse mapping,
clean/generalize/make it work everywhere list_cpus (which
already does that mapping) and then use that to do your thing.
It will have drawbacks you've listed above, but hopefully
that will clean up and reuse existing list_cpus.
(only this time, I'd build it around query-cpu-model-expansion,
which output is used by generic list_cpus)
[and here I'm asking to rewrite directly unrelated QEMU part yet again]
I'm afraid that list_cpus() is hard to be reused. All available CPU model names
are listed by list_cpus(). mc->valid_cpu_types[] are just part of them and
variable
on basis of boards. Generally speaking, we need a function to do reverse things
as to CPUClass::class_by_name(). So I would suggest to introduce
CPUClass::model_from_type(),
as below. Could you please suggest if it sounds reasonable to you?
- CPUClass::class_by_name() is modified to
char *CPUClass::model_to_type(const char *model)
- char *CPUClass::type_to_model(const char *type)
- CPUClass::type_to_model() is used in cpu_list() for every target when CPU
model name, fetched from CPU type name, is printed in xxx_cpu_list_entry()
- CPUClass::type_to_model() is reused in hw/core/machine.c to get the CPU
model name from CPU type names in mc->valid_cpu_types[].
instead of per target hooks (which are atm mostly open-coded in several places)
how about adding generic handler for cases 2,4:
cpu_type_to_model(typename)
cpu_suffix = re'-*-cpu'
if (class_exists(typename - cpu_suffix))
return typename - cpu_suffix
else if (class_exists(typename))
return typename
explode
that should work for translating valid_cpus typenames to cpumodel names
and once that in place cleanup all open-coded translations with it tree-wide
you can find those easily by:
git grep _CPU_TYPE_SUFFIX
git grep query_cpu_definitions
Thanks for the advice. I think it's enough for now since the CPU type
invalidation is currently done for arm/mips/riscv for now. On these
targets, the CPU type name is always the combination of the CPU model
name and suffix. I will add helper qemu/cpu.c::cpu_model_by_name()
as you suggested. Note that, the suffix can be gained by ("-"
CPU_RESOLVING_TYPE)
Yes, the newly added helper cpu_model_by_name() needs to be applied
to targets where query_cpu_definitions and cpu_list are defined.
Thanks,
Gavin