Re: [RFC PATCH v2 6/8] cpu: Declare cpu_has_work() in 'sysemu/tcg.h'

From: Claudio Fontana <cfontana@suse.de>
To: "Philippe Mathieu-Daudé" <f4bug@amsat.org>, qemu-devel@nongnu.org
Cc: Peter Maydell <peter.maydell@linaro.org>,
	Thomas Huth <thuth@redhat.com>,
	qemu-riscv@nongnu.org, Eduardo Habkost <ehabkost@redhat.com>,
	David Hildenbrand <david@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Richard Henderson <richard.henderson@linaro.org>,
	Laurent Vivier <laurent@vivier.eu>, Greg Kurz <groug@kaod.org>,
	qemu-s390x@nongnu.org, qemu-arm@nongnu.org, qemu-ppc@nongnu.org,
	Paolo Bonzini <pbonzini@redhat.com>,
	David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [RFC PATCH v2 6/8] cpu: Declare cpu_has_work() in 'sysemu/tcg.h'
Date: Mon, 8 Mar 2021 13:17:10 +0100	[thread overview]
Message-ID: <ddd0572a-bba2-62ac-27b8-4a7d04257695@suse.de> (raw)
In-Reply-To: <20210304222323.1954755-7-f4bug@amsat.org>

On 3/4/21 11:23 PM, Philippe Mathieu-Daudé wrote:
> We can only check if a vCPU has work with TCG.
> Move the cpu_has_work() prototype to "sysemu/tcg.h".
> 
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
> RFC: could another accelerator do that?
>      can we rename this tcg_vcpu_has_work()?
> ---
>  include/hw/core/cpu.h | 16 ----------------
>  include/sysemu/tcg.h  | 11 +++++++++++
>  accel/tcg/cpu-exec.c  |  7 +++++++
>  softmmu/cpus.c        |  1 +
>  4 files changed, 19 insertions(+), 16 deletions(-)
> 
> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
> index 1376e496a3f..66109bcca35 100644
> --- a/include/hw/core/cpu.h
> +++ b/include/hw/core/cpu.h
> @@ -670,22 +670,6 @@ CPUState *cpu_create(const char *typename);
>   */
>  const char *parse_cpu_option(const char *cpu_option);
>  
> -/**
> - * cpu_has_work:
> - * @cpu: The vCPU to check.
> - *
> - * Checks whether the CPU has work to do.
> - *
> - * Returns: %true if the CPU has work, %false otherwise.
> - */
> -static inline bool cpu_has_work(CPUState *cpu)
> -{
> -    CPUClass *cc = CPU_GET_CLASS(cpu);
> -
> -    g_assert(cc->has_work);
> -    return cc->has_work(cpu);
> -}
> -
>  /**
>   * qemu_cpu_is_self:
>   * @cpu: The vCPU to check against.
> diff --git a/include/sysemu/tcg.h b/include/sysemu/tcg.h
> index c16c13c3c69..3d46b0a7a93 100644
> --- a/include/sysemu/tcg.h
> +++ b/include/sysemu/tcg.h
> @@ -10,6 +10,7 @@
>  
>  #ifndef CONFIG_TCG
>  #define tcg_enabled() 0
> +#define cpu_has_work(cpu) false

email errors, so not sure if my previous message went off.

I am not convinced by this approach of _hiding_ the fact that cpu_has_work is TCG-only from the context where it is used.

When reading the actual code using this, how to get an immediate clue that this is TCG-only?

I think cpu_has_work should either be renamed to tcg_cpu_has_work(), thus providing the context in the name,
or it should not be visible/called for non-TCG at all, its call protected in some way (if (tcg_enabled() or ifdef or such..)

Ciao,

Claudio

>  #else
>  
>  void tcg_exec_init(unsigned long tb_size, int splitwx);
> @@ -26,6 +27,16 @@ extern bool tcg_allowed;
>  extern bool mttcg_enabled;
>  #define qemu_tcg_mttcg_enabled() (mttcg_enabled)
>  
> +/**
> + * cpu_has_work:
> + * @cpu: The vCPU to check.
> + *
> + * Checks whether the CPU has work to do.
> + *
> + * Returns: %true if the CPU has work, %false otherwise.
> + */
> +bool cpu_has_work(CPUState *cpu);
> +
>  #endif /* CONFIG_TCG */
>  
>  #endif
> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
> index 7e67ade35b9..b9ce36e59e2 100644
> --- a/accel/tcg/cpu-exec.c
> +++ b/accel/tcg/cpu-exec.c
> @@ -447,6 +447,13 @@ static inline TranslationBlock *tb_find(CPUState *cpu,
>      return tb;
>  }
>  
> +bool cpu_has_work(CPUState *cpu)
> +{
> +    CPUClass *cc = CPU_GET_CLASS(cpu);
> +
> +    return cc->has_work(cpu);
> +}
> +
>  static inline bool cpu_handle_halt(CPUState *cpu)
>  {
>      if (cpu->halted) {
> diff --git a/softmmu/cpus.c b/softmmu/cpus.c
> index a7ee431187a..548ab9236f1 100644
> --- a/softmmu/cpus.c
> +++ b/softmmu/cpus.c
> @@ -42,6 +42,7 @@
>  #include "sysemu/runstate.h"
>  #include "sysemu/cpu-timers.h"
>  #include "sysemu/whpx.h"
> +#include "sysemu/tcg.h"
>  #include "hw/boards.h"
>  #include "hw/hw.h"
>  
> 