[v7,05/13] cpu: Reclaim vCPU objects

Commit Message

Bharata B Rao Jan. 28, 2016, 5:49 a.m. UTC

From: Gu Zheng <[e-mail]>

In order to deal well with the kvm vcpus (which can not be removed without any
protection), we do not close KVM vcpu fd, just record and mark it as stopped
into a list, so that we can reuse it for the appending cpu hot-add request if
possible. It is also the approach that kvm guys suggested:
https://www.mail-archive.com/[e-mail]/msg102839.html

Signed-off-by: Chen Fan <[e-mail]>
Signed-off-by: Gu Zheng <[e-mail]>
Signed-off-by: Zhu Guihua <[e-mail]>
Signed-off-by: Bharata B Rao <[e-mail]>
               [- Explicit CPU_REMOVE() from qemu_kvm/tcg_destroy_vcpu()
                  isn't needed as it is done from cpu_exec_exit()
                - Use iothread mutex instead of global mutex during
                  destroy
                - Don't cleanup vCPU object from vCPU thread context
                  but leave it to the callers (device_add/device_del)]
Reviewed-by: David Gibson <[e-mail]>
---
 cpus.c               | 38 +++++++++++++++++++++++++++++++++++
 include/qom/cpu.h    | 10 +++++++++
 include/sysemu/kvm.h |  1 +
 kvm-all.c            | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 kvm-stub.c           |  5 +++++
 5 files changed, 110 insertions(+), 1 deletion(-)

Comments

Thomas Huth Feb. 19, 2016, 3:21 p.m. UTC | #1

On 28.01.2016 06:49, Bharata B Rao wrote:
> From: Gu Zheng <[e-mail]>
> 
> In order to deal well with the kvm vcpus (which can not be removed without any
> protection), we do not close KVM vcpu fd, just record and mark it as stopped
> into a list, so that we can reuse it for the appending cpu hot-add request if
> possible. It is also the approach that kvm guys suggested:
> https://www.mail-archive.com/[e-mail]/msg102839.html
> 
> Signed-off-by: Chen Fan <[e-mail]>
> Signed-off-by: Gu Zheng <[e-mail]>
> Signed-off-by: Zhu Guihua <[e-mail]>
> Signed-off-by: Bharata B Rao <[e-mail]>
>                [- Explicit CPU_REMOVE() from qemu_kvm/tcg_destroy_vcpu()
>                   isn't needed as it is done from cpu_exec_exit()
>                 - Use iothread mutex instead of global mutex during
>                   destroy
>                 - Don't cleanup vCPU object from vCPU thread context
>                   but leave it to the callers (device_add/device_del)]
> Reviewed-by: David Gibson <[e-mail]>
> ---
>  cpus.c               | 38 +++++++++++++++++++++++++++++++++++
>  include/qom/cpu.h    | 10 +++++++++
>  include/sysemu/kvm.h |  1 +
>  kvm-all.c            | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>  kvm-stub.c           |  5 +++++
>  5 files changed, 110 insertions(+), 1 deletion(-)
> 
> diff --git a/cpus.c b/cpus.c
> index 1e97cc4..c5631f0 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -953,6 +953,18 @@ void async_run_on_cpu(CPUState *cpu, void (*func)(void *data), void *data)
>      qemu_cpu_kick(cpu);
>  }
>  
> +static void qemu_kvm_destroy_vcpu(CPUState *cpu)
> +{
> +    if (kvm_destroy_vcpu(cpu) < 0) {
> +        error_report("kvm_destroy_vcpu failed");
> +        exit(EXIT_FAILURE);
> +    }
> +}
> +
> +static void qemu_tcg_destroy_vcpu(CPUState *cpu)
> +{

Will this be populated by a later patch in your series? If not, maybe
add a debugging statement here so that it is clear that there is a TODO
left here?

> +}
> +
>  static void flush_queued_work(CPUState *cpu)
>  {
>      struct qemu_work_item *wi;
> @@ -1053,6 +1065,11 @@ static void *qemu_kvm_cpu_thread_fn(void *arg)
>              }
>          }
>          qemu_kvm_wait_io_event(cpu);
> +        if (cpu->exit && !cpu_can_run(cpu)) {
> +            qemu_kvm_destroy_vcpu(cpu);
> +            qemu_mutex_unlock_iothread();
> +            return NULL;
> +        }
>      }

You could increase readability of the code by changing the condition of
the loop instead - currently it is a "while (1)" ... you could turn that
into a "do { ... } while (!cpu->exit || cpu_can_run(cpu))" and then
destroy the cpu after the loop.

>      return NULL;
...
> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> index 2e5229d..32a2c71 100644
> --- a/include/qom/cpu.h
> +++ b/include/qom/cpu.h
> @@ -232,6 +232,7 @@ struct kvm_run;
>   * @halted: Nonzero if the CPU is in suspended state.
>   * @stop: Indicates a pending stop request.
>   * @stopped: Indicates the CPU has been artificially stopped.
> + * @exit: Indicates the CPU has exited due to an unplug operation.

There is also a "exit_request" member in this struct already ... maybe
you could name your new variable differently to avoid confusion?
Something like "remove_request" or "unplug_request" ?

>   * @crash_occurred: Indicates the OS reported a crash (panic) for this CPU
>   * @tcg_exit_req: Set to force TCG to stop executing linked TBs for this
>   *           CPU and return to its top level loop.
> @@ -284,6 +285,7 @@ struct CPUState {
>      bool created;
>      bool stop;
>      bool stopped;
> +    bool exit;
>      bool crash_occurred;
>      bool exit_request;
>      uint32_t interrupt_request;
...

Apart from that, the patch looks fine to me.

 Thomas

Patch

diff --git a/cpus.c b/cpus.c
index 1e97cc4..c5631f0 100644
--- a/cpus.c
+++ b/cpus.c
@@ -953,6 +953,18 @@  void async_run_on_cpu(CPUState *cpu, void (*func)(void *data), void *data)
     qemu_cpu_kick(cpu);
 }
 
+static void qemu_kvm_destroy_vcpu(CPUState *cpu)
+{
+    if (kvm_destroy_vcpu(cpu) < 0) {
+        error_report("kvm_destroy_vcpu failed");
+        exit(EXIT_FAILURE);
+    }
+}
+
+static void qemu_tcg_destroy_vcpu(CPUState *cpu)
+{
+}
+
 static void flush_queued_work(CPUState *cpu)
 {
     struct qemu_work_item *wi;
@@ -1053,6 +1065,11 @@  static void *qemu_kvm_cpu_thread_fn(void *arg)
             }
         }
         qemu_kvm_wait_io_event(cpu);
+        if (cpu->exit && !cpu_can_run(cpu)) {
+            qemu_kvm_destroy_vcpu(cpu);
+            qemu_mutex_unlock_iothread();
+            return NULL;
+        }
     }
 
     return NULL;
@@ -1108,6 +1125,7 @@  static void tcg_exec_all(void);
 static void *qemu_tcg_cpu_thread_fn(void *arg)
 {
     CPUState *cpu = arg;
+    CPUState *remove_cpu = NULL;
 
     rcu_register_thread();
 
@@ -1145,6 +1163,16 @@  static void *qemu_tcg_cpu_thread_fn(void *arg)
             }
         }
         qemu_tcg_wait_io_event(QTAILQ_FIRST(&cpus));
+        CPU_FOREACH(cpu) {
+            if (cpu->exit && !cpu_can_run(cpu)) {
+                remove_cpu = cpu;
+                break;
+            }
+        }
+        if (remove_cpu) {
+            qemu_tcg_destroy_vcpu(remove_cpu);
+            remove_cpu = NULL;
+        }
     }
 
     return NULL;
@@ -1301,6 +1329,13 @@  void resume_all_vcpus(void)
     }
 }
 
+void cpu_remove(CPUState *cpu)
+{
+    cpu->stop = true;
+    cpu->exit = true;
+    qemu_cpu_kick(cpu);
+}
+
 /* For temporary buffers for forming a name */
 #define VCPU_THREAD_NAME_SIZE 16
 
@@ -1517,6 +1552,9 @@  static void tcg_exec_all(void)
                 break;
             }
         } else if (cpu->stop || cpu->stopped) {
+            if (cpu->exit) {
+                next_cpu = CPU_NEXT(cpu);
+            }
             break;
         }
     }
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 2e5229d..32a2c71 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -232,6 +232,7 @@  struct kvm_run;
  * @halted: Nonzero if the CPU is in suspended state.
  * @stop: Indicates a pending stop request.
  * @stopped: Indicates the CPU has been artificially stopped.
+ * @exit: Indicates the CPU has exited due to an unplug operation.
  * @crash_occurred: Indicates the OS reported a crash (panic) for this CPU
  * @tcg_exit_req: Set to force TCG to stop executing linked TBs for this
  *           CPU and return to its top level loop.
@@ -284,6 +285,7 @@  struct CPUState {
     bool created;
     bool stop;
     bool stopped;
+    bool exit;
     bool crash_occurred;
     bool exit_request;
     uint32_t interrupt_request;
@@ -751,6 +753,14 @@  void cpu_exit(CPUState *cpu);
 void cpu_resume(CPUState *cpu);
 
 /**
+ * cpu_remove:
+ * @cpu: The CPU to remove.
+ *
+ * Requests the CPU to be removed.
+ */
+void cpu_remove(CPUState *cpu);
+
+/**
  * qemu_init_vcpu:
  * @cpu: The vCPU to initialize.
  *
diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
index 7741f91..7324fa9 100644
--- a/include/sysemu/kvm.h
+++ b/include/sysemu/kvm.h
@@ -218,6 +218,7 @@  int kvm_has_intx_set_mask(void);
 
 int kvm_init_vcpu(CPUState *cpu);
 int kvm_cpu_exec(CPUState *cpu);
+int kvm_destroy_vcpu(CPUState *cpu);
 
 #ifdef NEED_CPU_H
 
diff --git a/kvm-all.c b/kvm-all.c
index 9148889..699c1ce 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -62,6 +62,12 @@ 
 
 #define KVM_MSI_HASHTAB_SIZE    256
 
+struct KVMParkedVcpu {
+    unsigned long vcpu_id;
+    int kvm_fd;
+    QLIST_ENTRY(KVMParkedVcpu) node;
+};
+
 struct KVMState
 {
     AccelState parent_obj;
@@ -95,6 +101,7 @@  struct KVMState
     QTAILQ_HEAD(msi_hashtab, KVMMSIRoute) msi_hashtab[KVM_MSI_HASHTAB_SIZE];
 #endif
     KVMMemoryListener memory_listener;
+    QLIST_HEAD(, KVMParkedVcpu) kvm_parked_vcpus;
 };
 
 KVMState *kvm_state;
@@ -238,6 +245,53 @@  static int kvm_set_user_memory_region(KVMMemoryListener *kml, KVMSlot *slot)
     return kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
 }
 
+int kvm_destroy_vcpu(CPUState *cpu)
+{
+    KVMState *s = kvm_state;
+    long mmap_size;
+    struct KVMParkedVcpu *vcpu = NULL;
+    int ret = 0;
+
+    DPRINTF("kvm_destroy_vcpu\n");
+
+    mmap_size = kvm_ioctl(s, KVM_GET_VCPU_MMAP_SIZE, 0);
+    if (mmap_size < 0) {
+        ret = mmap_size;
+        DPRINTF("KVM_GET_VCPU_MMAP_SIZE failed\n");
+        goto err;
+    }
+
+    ret = munmap(cpu->kvm_run, mmap_size);
+    if (ret < 0) {
+        goto err;
+    }
+
+    vcpu = g_malloc0(sizeof(*vcpu));
+    vcpu->vcpu_id = kvm_arch_vcpu_id(cpu);
+    vcpu->kvm_fd = cpu->kvm_fd;
+    QLIST_INSERT_HEAD(&kvm_state->kvm_parked_vcpus, vcpu, node);
+err:
+    return ret;
+}
+
+static int kvm_get_vcpu(KVMState *s, unsigned long vcpu_id)
+{
+    struct KVMParkedVcpu *cpu;
+
+    QLIST_FOREACH(cpu, &s->kvm_parked_vcpus, node) {
+        if (cpu->vcpu_id == vcpu_id) {
+            int kvm_fd;
+
+            QLIST_REMOVE(cpu, node);
+            kvm_fd = cpu->kvm_fd;
+            g_free(cpu);
+            return kvm_fd;
+        }
+    }
+
+    return kvm_vm_ioctl(s, KVM_CREATE_VCPU, (void *)vcpu_id);
+}
+
 int kvm_init_vcpu(CPUState *cpu)
 {
     KVMState *s = kvm_state;
@@ -246,7 +300,7 @@  int kvm_init_vcpu(CPUState *cpu)
 
     DPRINTF("kvm_init_vcpu\n");
 
-    ret = kvm_vm_ioctl(s, KVM_CREATE_VCPU, (void *)kvm_arch_vcpu_id(cpu));
+    ret = kvm_get_vcpu(s, kvm_arch_vcpu_id(cpu));
     if (ret < 0) {
         DPRINTF("kvm_create_vcpu failed\n");
         goto err;
@@ -1509,6 +1563,7 @@  static int kvm_init(MachineState *ms)
 #ifdef KVM_CAP_SET_GUEST_DEBUG
     QTAILQ_INIT(&s->kvm_sw_breakpoints);
 #endif
+    QLIST_INIT(&s->kvm_parked_vcpus);
     s->vmfd = -1;
     s->fd = qemu_open("/dev/kvm", O_RDWR);
     if (s->fd == -1) {
diff --git a/kvm-stub.c b/kvm-stub.c
index dc97a5e..0b39456 100644
--- a/kvm-stub.c
+++ b/kvm-stub.c
@@ -32,6 +32,11 @@  bool kvm_allowed;
 bool kvm_readonly_mem_allowed;
 bool kvm_ioeventfd_any_length_allowed;
 
+int kvm_destroy_vcpu(CPUState *cpu)
+{
+    return -ENOSYS;
+}
+
 int kvm_init_vcpu(CPUState *cpu)
 {
     return -ENOSYS;