Re: [PATCH-for-9.0 0/2] target/monitor: Deprecate 'info tlb/mem' in favor of 'info mmu'
+Alex/Daniel
On 20/3/24 17:53, Peter Maydell wrote:
On Wed, 20 Mar 2024 at 16:40, Philippe Mathieu-Daudé
<philmd(a)linaro.org> wrote:
>
> 'info tlb' and 'info mem' commands don't scale in heterogeneous
> emulation. They will be reworked after the next release, hidden
> behind the 'info mmu' command. It is not too late to deprecate
> commands, so add the 'info mmu' command as wrapper to the other
> ones, but already deprecate them.
>
> Philippe Mathieu-Daudé (2):
> target/monitor: Introduce 'info mmu' command
> target/monitor: Deprecate 'info tlb' and 'info mem' commands
This seems to replace "info tlb" and "info mem" with "info mmu
-t"
and "info mmu -m", but it doesn't really say anything about:
* what the difference is between these two things
I really don't know; I'm only trying to keep the monitor interface
identical.
* which targets implement which and why
This one is easy to answer:
#if defined(TARGET_I386) || defined(TARGET_SH4) || defined(TARGET_SPARC)
|| \
defined(TARGET_PPC) || defined(TARGET_XTENSA) || defined(TARGET_M68K)
{
.name = "tlb",
#if defined(TARGET_I386) || defined(TARGET_RISCV)
{
.name = "mem",
* what the plan is for the future
My problem is with linking a single QEMU binary, as these two symbols
(hmp_info_mem and hmp_info_tlb) clash.
Luckily for me these are the only 2 implemented by more then one target:
$ git grep TARGET_ -- hmp-commands*
hmp-commands-info.hx:116:#if defined(TARGET_I386)
hmp-commands-info.hx:225:#if defined(TARGET_I386) || defined(TARGET_SH4)
|| defined(TARGET_SPARC) || \
hmp-commands-info.hx:226: defined(TARGET_PPC) ||
defined(TARGET_XTENSA) || defined(TARGET_M68K)
hmp-commands-info.hx:241:#if defined(TARGET_I386) || defined(TARGET_RISCV)
hmp-commands-info.hx:729:#if defined(TARGET_S390X)
hmp-commands-info.hx:744:#if defined(TARGET_S390X)
hmp-commands-info.hx:828:#if defined(TARGET_I386)
hmp-commands-info.hx:882:#if defined(TARGET_I386)
hmp-commands.hx:1126:#if defined(TARGET_S390X)
hmp-commands.hx:1141:#if defined(TARGET_S390X)
hmp-commands.hx:1489:#if defined(TARGET_I386)
All the other ones are only implemented by a single target, so not a
problem for now.
I'm indeed only postponing the problem, without looking at what
this code does. I did it adding hmp_info_mmu_tlb/mem hooks in
TCGCPUOps ("hw/core/tcg-cpu-ops.h"), so the command can be
dispatched per target vcpu as target-agnostic code in
monitor/hmp-cmds.c:
+#include "hw/core/tcg-cpu-ops.h"
+
+static void hmp_info_mmu_tlb(Monitor *mon, CPUState *cpu)
+{
+ const TCGCPUOps *tcg_ops = cpu->cc->tcg_ops;
+
+ if (tcg_ops->hmp_info_mmu_tlb) {
+ tcg_ops->hmp_info_mmu_tlb(mon, cpu_env(cpu));
+ } else {
+ monitor_puts(mon, "No per-CPU information available on this
target\n");
+ }
+}
I am definitely not a fan of either of these commands, because
(as we currently implement them) they effectively require each
target architecture to implement a second copy of the page table
walking code. But before we can deprecate them we need to be
pretty sure that "info mmu" is what we want to replace them with.
An alternative is to just deprecate them, without adding "info mmu" :)
It is OK to un-deprecate stuff if we realize its usefulness.
Regards,
Phil.