Re: [Qemu-devel] [RFC v3 09/13] cpus.c: introduce simple callback support

[alvise rigo]

On Fri, Jul 10, 2015 at 11:53 AM, Frederic Konrad
<address@hidden> wrote:
> On 10/07/2015 11:47, alvise rigo wrote:
>>
>> I tried to use it, but it would then create a deadlock at a very early
>> stage of the stress test.
>> The problem is likely related to the fact that flush_queued_work
>> happens with the global mutex locked.
>>
>> As Frederick suggested, we can use the newly introduced
>> flush_queued_safe_work for this.
>>
>> Regards,
>> alvise
>
>
> It depends on the purpose.
>
> async safe work will requires all VCPU to be exited (eg: like your
> rendez-vous).
> async work doesn't it will just do the work when it's outside cpu-exec().

I guess that still this should work. If you look at helper_le_ldlink_name, only
the vCPUs in cpu-exec() receive a rendez-vous request while *all*
vCPUs are asked to perform a TLB flush.

alvise

>
> Theorically this is required only when a VCPU flushes the TLB of an other
> VCPU.
> That's the behaviour in tlb_flush_all tlb_page_flush_all. The "normal"
> tlb_flush should
> just work as it only plays with it's own CPUState.
>
> Fred
>
>
>> On Fri, Jul 10, 2015 at 11:36 AM, Paolo Bonzini <address@hidden>
>> wrote:
>>>
>>>
>>> On 10/07/2015 10:23, Alvise Rigo wrote:
>>>>
>>>> In order to perfom "lazy" TLB invalidation requests, introduce a
>>>> queue of callbacks at every vCPU disposal that will be fired just
>>>> before entering the next TB.
>>>>
>>>> Suggested-by: Jani Kokkonen <address@hidden>
>>>> Suggested-by: Claudio Fontana <address@hidden>
>>>> Signed-off-by: Alvise Rigo <address@hidden>
>>>
>>> Why is async_run_on_cpu not enough?
>>>
>>> Paolo
>>>
>>>> ---
>>>>   cpus.c            | 34 ++++++++++++++++++++++++++++++++++
>>>>   exec.c            |  1 +
>>>>   include/qom/cpu.h | 20 ++++++++++++++++++++
>>>>   3 files changed, 55 insertions(+)
>>>>
>>>> diff --git a/cpus.c b/cpus.c
>>>> index f4d938e..b9f0329 100644
>>>> --- a/cpus.c
>>>> +++ b/cpus.c
>>>> @@ -1421,6 +1421,7 @@ static int tcg_cpu_exec(CPUArchState *env)
>>>>           cpu->icount_extra = count;
>>>>       }
>>>>       qemu_mutex_unlock_iothread();
>>>> +    cpu_exit_callbacks_call_all(cpu);
>>>>       ret = cpu_exec(env);
>>>>       cpu->tcg_executing = 0;
>>>>
>>>> @@ -1469,6 +1470,39 @@ static void tcg_exec_all(CPUState *cpu)
>>>>       cpu->exit_request = 0;
>>>>   }
>>>>
>>>> +void cpu_exit_callback_add(CPUState *cpu, CPUExitCallback callback,
>>>> +                           void *opaque)
>>>> +{
>>>> +    CPUExitCB *cb;
>>>> +
>>>> +    cb = g_malloc(sizeof(*cb));
>>>> +    cb->callback = callback;
>>>> +    cb->opaque = opaque;
>>>> +
>>>> +    qemu_mutex_lock(&cpu->exit_cbs.mutex);
>>>> +    QTAILQ_INSERT_TAIL(&cpu->exit_cbs.exit_callbacks, cb, entry);
>>>> +    qemu_mutex_unlock(&cpu->exit_cbs.mutex);
>>>> +}
>>>> +
>>>> +void cpu_exit_callbacks_call_all(CPUState *cpu)
>>>> +{
>>>> +    CPUExitCB *cb, *next;
>>>> +
>>>> +    if (QTAILQ_EMPTY(&cpu->exit_cbs.exit_callbacks)) {
>>>> +        return;
>>>> +    }
>>>> +
>>>> +    QTAILQ_FOREACH_SAFE(cb, &cpu->exit_cbs.exit_callbacks, entry, next)
>>>> {
>>>> +        cb->callback(cpu, cb->opaque);
>>>> +
>>>> +        /* one-shot callbacks, remove it after using it */
>>>> +        qemu_mutex_lock(&cpu->exit_cbs.mutex);
>>>> +        QTAILQ_REMOVE(&cpu->exit_cbs.exit_callbacks, cb, entry);
>>>> +        g_free(cb);
>>>> +        qemu_mutex_unlock(&cpu->exit_cbs.mutex);
>>>> +    }
>>>> +}
>>>> +
>>>>   void list_cpus(FILE *f, fprintf_function cpu_fprintf, const char
>>>> *optarg)
>>>>   {
>>>>       /* XXX: implement xxx_cpu_list for targets that still miss it */
>>>> diff --git a/exec.c b/exec.c
>>>> index 51958ed..322f2c6 100644
>>>> --- a/exec.c
>>>> +++ b/exec.c
>>>> @@ -531,6 +531,7 @@ void cpu_exec_init(CPUArchState *env)
>>>>       cpu->numa_node = 0;
>>>>       QTAILQ_INIT(&cpu->breakpoints);
>>>>       QTAILQ_INIT(&cpu->watchpoints);
>>>> +    QTAILQ_INIT(&cpu->exit_cbs.exit_callbacks);
>>>>   #ifndef CONFIG_USER_ONLY
>>>>       cpu->as = &address_space_memory;
>>>>       cpu->thread_id = qemu_get_thread_id();
>>>> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
>>>> index 8d121b3..0ec020b 100644
>>>> --- a/include/qom/cpu.h
>>>> +++ b/include/qom/cpu.h
>>>> @@ -201,6 +201,24 @@ typedef struct CPUWatchpoint {
>>>>       QTAILQ_ENTRY(CPUWatchpoint) entry;
>>>>   } CPUWatchpoint;
>>>>
>>>> +/* vCPU exit callbacks */
>>>> +typedef void (*CPUExitCallback)(CPUState *cpu, void *opaque);
>>>> +struct CPUExitCBs {
>>>> +    QemuMutex mutex;
>>>> +    QTAILQ_HEAD(exit_callbacks_head, CPUExitCB) exit_callbacks;
>>>> +};
>>>> +
>>>> +typedef struct CPUExitCB {
>>>> +    CPUExitCallback callback;
>>>> +    void *opaque;
>>>> +
>>>> +    QTAILQ_ENTRY(CPUExitCB) entry;
>>>> +} CPUExitCB;
>>>> +
>>>> +void cpu_exit_callback_add(CPUState *cpu, CPUExitCallback callback,
>>>> +                           void *opaque);
>>>> +void cpu_exit_callbacks_call_all(CPUState *cpu);
>>>> +
>>>>   /* Rendezvous support */
>>>>   #define TCG_RDV_POLLING_PERIOD 10
>>>>   typedef struct CpuExitRendezvous {
>>>> @@ -305,6 +323,8 @@ struct CPUState {
>>>>
>>>>       void *opaque;
>>>>
>>>> +    /* One-shot callbacks for stopping requests. */
>>>> +    struct CPUExitCBs exit_cbs;
>>>>       volatile int pending_rdv;
>>>>
>>>>       /* In order to avoid passing too many arguments to the MMIO
>>>> helpers,
>>>>
>