Re: [Qemu-devel] Re: [PATCH 02/21] introduce QEMUAccel and fill it with interrupt specific driver

["Glauber Costa" <glommer@gmail.com>]

On Wed, Oct 15, 2008 at 6:20 PM, Anthony Liguori <aliguori@us.ibm.com> wrote:
> Glauber Costa wrote:
>>
>> From: Glauber Costa <gcosta@redhat.com>
>>
>> This patch introduces QEMUAccel, a placeholder for function pointers
>> that aims at helping qemu to abstract accelerators such as kqemu and
>> kvm (actually, the 'accelerator' name was proposed by avi kivity, since
>> he loves referring to kvm that way).
>>
>> To begin with, the accelerator is given the opportunity to register a
>> cpu_interrupt function, to be called after the raw cpu_interrupt.
>> This has the side effect of, for the kqemu accelerator, calling
>> kqemu_cpu_interrupt
>> everytime, which didn't use to happen. But looking at the code, this seems
>> safe to me.
>>
>> This patch applies on raw qemu.
>>
>> Signed-off-by: Glauber Costa <glommer@redhat.com>
>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@siemens.com>
>> ---
>>  Makefile.target |    2 +-
>>  accel.c         |   17 +++++++++++++++++
>>  accel.h         |   20 ++++++++++++++++++++
>>  exec.c          |    3 +++
>>  kqemu.c         |    9 +++++++++
>>  vl.c            |   17 +++++------------
>>  6 files changed, 55 insertions(+), 13 deletions(-)
>>  create mode 100644 accel.c
>>  create mode 100644 accel.h
>>
>> diff --git a/Makefile.target b/Makefile.target
>> index e2edf9d..623ecd8 100644
>> --- a/Makefile.target
>> +++ b/Makefile.target
>> @@ -188,7 +188,7 @@ all: $(PROGS)
>>  #########################################################
>>  # cpu emulator library
>>  LIBOBJS=exec.o kqemu.o translate-all.o cpu-exec.o\
>> -        translate.o host-utils.o
>> +        translate.o host-utils.o accel.o
>>  ifdef CONFIG_DYNGEN_OP
>>  exec.o: dyngen-opc.h
>>  LIBOBJS+=op.o
>> diff --git a/accel.c b/accel.c
>> new file mode 100644
>> index 0000000..d30460d
>> --- /dev/null
>> +++ b/accel.c
>> @@ -0,0 +1,17 @@
>> +#include "hw/hw.h"
>> +#include "accel.h"
>> +
>> +QEMUAccel *current_accel;
>> +
>> +int _accel_nop(void)
>> +{
>> +    return 0;
>> +}
>> +
>> +#define accel_nop ((void *)_accel_nop)
>> +
>> +/* Accelerator wrapper for the no-accel (raw qemu) case */
>> +QEMUAccel noaccel = {
>> +    .cpu_interrupt = accel_nop,
>> +};
>> +
>> diff --git a/accel.h b/accel.h
>> new file mode 100644
>> index 0000000..8e5ddc6
>> --- /dev/null
>> +++ b/accel.h
>> @@ -0,0 +1,20 @@
>> +#ifndef _ACCEL_H_
>> +#define _ACCEL_H_
>> +
>> +typedef struct QEMUAccel {
>> +    void (*cpu_interrupt)(CPUState *env);
>> +} QEMUAccel;
>> +
>> +extern QEMUAccel *current_accel;
>> +extern QEMUAccel noaccel;
>> +
>> +static inline void register_qemu_accel(QEMUAccel *accel)
>> +{
>> +    current_accel = accel;
>> +}
>> +
>> +static inline void accel_cpu_interrupt(CPUState *env)
>> +{
>> +    current_accel->cpu_interrupt(env);
>> +}
>> +#endif
>> diff --git a/exec.c b/exec.c
>> index 1cad0be..21253cc 100644
>> --- a/exec.c
>> +++ b/exec.c
>> @@ -43,6 +43,8 @@
>>  #include <qemu.h>
>>  #endif
>>
>> +#include "accel.h"
>> +
>>  //#define DEBUG_TB_INVALIDATE
>>  //#define DEBUG_FLUSH
>>  //#define DEBUG_TLB
>> @@ -1430,6 +1432,7 @@ void cpu_single_step(CPUState *env, int enabled)
>>         tb_flush(env);
>>     }
>>  #endif
>> +    accel_cpu_interrupt(env);
>>  }
>>
>>  /* enable or disable low levels log */
>> diff --git a/kqemu.c b/kqemu.c
>> index 9b52237..87c06cd 100644
>> --- a/kqemu.c
>> +++ b/kqemu.c
>> @@ -50,6 +50,7 @@
>>  #include <unistd.h>
>>  #include <fcntl.h>
>>  #include "kqemu.h"
>> +#include "accel.h"
>>
>>  #ifdef _WIN32
>>  #define KQEMU_DEVICE "\\\\.\\kqemu"
>> @@ -150,6 +151,8 @@ static void kqemu_update_cpuid(CPUState *env)
>>        accelerated code */
>>  }
>>
>> +QEMUAccel kqemu_accel;
>> +
>>  int kqemu_start(void)
>>  {
>>     struct kqemu_init kinit;
>> @@ -232,6 +235,7 @@ int kqemu_start(void)
>>     }
>>     nb_pages_to_flush = 0;
>>     nb_ram_pages_to_update = 0;
>> +    register_qemu_accel(&kqemu_accel);
>>
>>     qpi_init();
>>     return 0;
>> @@ -243,6 +247,11 @@ void kqemu_init_env(CPUState *env)
>>     env->kqemu_enabled = kqemu_allowed;
>>  }
>>
>> +QEMUAccel kqemu_accel = {
>> +    .cpu_interrupt = kqemu_cpu_interrupt,
>> +};
>>
>
> The hook kqemu uses is for CPU_INTERRUPT_EXIT which is basically intended to
> allow IO to run.  The fact that it's done via cpu_interrupt is somewhat
> hackish.
>
> I think a better hook would be something like run_io_handlers.  Since this
> is called from signal handlers, we have to be clear that this code needs to
> be signal safe.  This is compared to say a generic cpu_interrupt hook which
> doesn't necessarily need to be signal safe.

KVM has code in cpu interrupt. So even if we move kqemu elsewhere,
this one might still be useful.

> Regards,
>
> Anthony Liguori
>
>
>



-- 
Glauber  Costa.
"Free as in Freedom"
http://glommer.net

"The less confident you are, the more serious you have to act."