[Qemu-devel] [PATCHv3 0/4] ] add query-cpu-fast and related s390 changes

[Qemu-devel] [PATCHv3 0/4] ] add query-cpu-fast and related s390 changes

[Viktor Mihajlovski]

This series consolidates patches around a performance issue
caused by the usage of QMP query-cpus.

A performance issue was found in an OpenStack environment, where
ceilometer was collecting domain statistics with libvirt. The domain
statistics reported by libvirt include the vCPU halted state, which 
in turn is retrieved with QMP query-cpus.

This causes two issues:
1. Performance: on most architectures query-cpus needs to issue a KVM ioctl
   to find out whether a vCPU was halted. This is not the case for s390
   but query-cpus is always causing the vCPU to exit the VM.

2. Semantics: on x86 and other architectures, halted is a highly transient
   state, which is likely to have already changed shortly after the state
   information has been retrieved. This is not the case for s390, where
   halted is an indication that the vCPU is stopped, meaning its not
   available to the guest operating system until it has been restarted.

The following patches help to alleviate the issues:

Patch 1/4:
  Adds architecture specific data to the QMP CpuInfo type, exposing
  the existing s390 cpu-state in QMP. The cpu-state is a representation
  more adequate than the ambiguous 'halted' condition.

Patch 2/4:
  Adds a new QMP function query-cpus-fast, which will only retrieve
  vCPU information that can be obtained without interrupting the
  vCPUs of a running VM. It introduces a new return type CpuInfoFast
  with the subset of fields meeting this condition. Specifically, the
  halted state is not part of CpuInfoFast. QMP clients like libvirt
  are encouraged to switch to the new API for vCPU information.

Patch 3/4:
  Adds the s390-specific cpu state to CpuInfoFast, allowing management
  apps to find out whether a vCPU is in the stopped state. This extension
  leads to a partial duplication of field definitions from CpuInfo
  to CpuInfoFast. This should be tolerable if CpuInfo is deprecated and
  eventually removed.

Patch 4/4 (NEW):
  Starts the deprecation of query-cpus and hmp 'info cpus'. It wouldn't
  hurt to have QAPI and HMP maintainer reviews for this.

Series v2 -> v3:
Overall: Added r-b's and a-b's.

Patch 2/4:
  o Fixed commit message with respect to the halted field
    disposition.
  o Fixed grammar in qapi-schema documentation.

Patch 3/4:
  o Use CpuInfoS390 type for both query-cpus and query-cpus-fast per
    Eric Blake's comment.
  o Dropped 'duplication blurb' from commit message as it doesn't
    provide relevant information other than query-cpus should be
    deprecated, which is done in the next patch now.

Series v1 -> v2:
Patch 2/3:
  o Changed formatting of hmp info cpus_fast to match that of
    info cpus. This makes it easier for clients to switch to
    the fast call.

Patch 3/3:
  o Same formatting change for info cpus_fast as in 2/3, only
    for s390-specific cpu state.

Luiz Capitulino (1):
  qmp: add query-cpus-fast

Viktor Mihajlovski (3):
  qmp: expose s390-specific CPU info
  qmp: add architecture specific cpu data for query-cpus-fast
  qemu-doc: deprecate query-cpus and info cpus

 cpus.c                     |  54 +++++++++++++++++++++
 hmp-commands-info.hx       |  18 ++++++-
 hmp.c                      |  28 +++++++++++
 hmp.h                      |   1 +
 hw/intc/s390_flic.c        |   4 +-
 hw/s390x/s390-virtio-ccw.c |   2 +-
 qapi-schema.json           | 115 ++++++++++++++++++++++++++++++++++++++++++++-
 qemu-doc.texi              |  10 ++++
 target/s390x/cpu.c         |  24 +++++-----
 target/s390x/cpu.h         |   7 +--
 target/s390x/kvm.c         |   8 ++--
 target/s390x/sigp.c        |  38 +++++++--------
 12 files changed, 262 insertions(+), 47 deletions(-)

-- 
1.9.1

[Qemu-devel] [PATCHv3 1/4] qmp: expose s390-specific CPU info

[Viktor Mihajlovski]

Presently s390x is the only architecture not exposing specific
CPU information via QMP query-cpus. Upstream discussion has shown
that it could make sense to report the architecture specific CPU
state, e.g. to detect that a CPU has been stopped.

With this change the output of query-cpus will look like this on
s390:

   [
     {"arch": "s390", "current": true,
      "props": {"core-id": 0}, "cpu-state": "operating", "CPU": 0,
      "qom_path": "/machine/unattached/device[0]",
      "halted": false, "thread_id": 63115},
     {"arch": "s390", "current": false,
      "props": {"core-id": 1}, "cpu-state": "stopped", "CPU": 1,
      "qom_path": "/machine/unattached/device[1]",
      "halted": true, "thread_id": 63116}
   ]

Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
Acked-by: Eric Blake <eblake@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
 cpus.c                     |  6 ++++++
 hmp.c                      |  4 ++++
 hw/intc/s390_flic.c        |  4 ++--
 hw/s390x/s390-virtio-ccw.c |  2 +-
 qapi-schema.json           | 28 +++++++++++++++++++++++++++-
 target/s390x/cpu.c         | 24 ++++++++++++------------
 target/s390x/cpu.h         |  7 ++-----
 target/s390x/kvm.c         |  8 ++++----
 target/s390x/sigp.c        | 38 +++++++++++++++++++-------------------
 9 files changed, 77 insertions(+), 44 deletions(-)

diff --git a/cpus.c b/cpus.c
index f298b65..6006931 100644
--- a/cpus.c
+++ b/cpus.c
@@ -2100,6 +2100,9 @@ CpuInfoList *qmp_query_cpus(Error **errp)
 #elif defined(TARGET_TRICORE)
         TriCoreCPU *tricore_cpu = TRICORE_CPU(cpu);
         CPUTriCoreState *env = &tricore_cpu->env;
+#elif defined(TARGET_S390X)
+        S390CPU *s390_cpu = S390_CPU(cpu);
+        CPUS390XState *env = &s390_cpu->env;
 #endif
 
         cpu_synchronize_state(cpu);
@@ -2127,6 +2130,9 @@ CpuInfoList *qmp_query_cpus(Error **errp)
 #elif defined(TARGET_TRICORE)
         info->value->arch = CPU_INFO_ARCH_TRICORE;
         info->value->u.tricore.PC = env->PC;
+#elif defined(TARGET_S390X)
+        info->value->arch = CPU_INFO_ARCH_S390;
+        info->value->u.s390.cpu_state = env->cpu_state;
 #else
         info->value->arch = CPU_INFO_ARCH_OTHER;
 #endif
diff --git a/hmp.c b/hmp.c
index 7870d6a..a6b94b7 100644
--- a/hmp.c
+++ b/hmp.c
@@ -392,6 +392,10 @@ void hmp_info_cpus(Monitor *mon, const QDict *qdict)
         case CPU_INFO_ARCH_TRICORE:
             monitor_printf(mon, " PC=0x%016" PRIx64, cpu->value->u.tricore.PC);
             break;
+        case CPU_INFO_ARCH_S390:
+            monitor_printf(mon, " state=%s",
+                           CpuS390State_str(cpu->value->u.s390.cpu_state));
+            break;
         default:
             break;
         }
diff --git a/hw/intc/s390_flic.c b/hw/intc/s390_flic.c
index a85a149..5f8168f 100644
--- a/hw/intc/s390_flic.c
+++ b/hw/intc/s390_flic.c
@@ -192,8 +192,8 @@ static void qemu_s390_flic_notify(uint32_t type)
         cs->interrupt_request |= CPU_INTERRUPT_HARD;
 
         /* ignore CPUs that are not sleeping */
-        if (s390_cpu_get_state(cpu) != CPU_STATE_OPERATING &&
-            s390_cpu_get_state(cpu) != CPU_STATE_LOAD) {
+        if (s390_cpu_get_state(cpu) != S390_CPU_STATE_OPERATING &&
+            s390_cpu_get_state(cpu) != S390_CPU_STATE_LOAD) {
             continue;
         }
 
diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index 4abbe89..4d0c3de 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -368,7 +368,7 @@ static void s390_machine_reset(void)
 
     /* all cpus are stopped - configure and start the ipl cpu only */
     s390_ipl_prepare_cpu(ipl_cpu);
-    s390_cpu_set_state(CPU_STATE_OPERATING, ipl_cpu);
+    s390_cpu_set_state(S390_CPU_STATE_OPERATING, ipl_cpu);
 }
 
 static void s390_machine_device_plug(HotplugHandler *hotplug_dev,
diff --git a/qapi-schema.json b/qapi-schema.json
index 0262b9f..94d560e 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -410,10 +410,12 @@
 # An enumeration of cpu types that enable additional information during
 # @query-cpus.
 #
+# @s390: since 2.12
+#
 # Since: 2.6
 ##
 { 'enum': 'CpuInfoArch',
-  'data': ['x86', 'sparc', 'ppc', 'mips', 'tricore', 'other' ] }
+  'data': ['x86', 'sparc', 'ppc', 'mips', 'tricore', 's390', 'other' ] }
 
 ##
 # @CpuInfo:
@@ -452,6 +454,7 @@
             'ppc': 'CpuInfoPPC',
             'mips': 'CpuInfoMIPS',
             'tricore': 'CpuInfoTricore',
+            's390': 'CpuInfoS390',
             'other': 'CpuInfoOther' } }
 
 ##
@@ -522,6 +525,29 @@
 { 'struct': 'CpuInfoOther', 'data': { } }
 
 ##
+# @CpuS390State:
+#
+# An enumeration of cpu states that can be assumed by a virtual
+# S390 CPU
+#
+# Since: 2.12
+##
+{ 'enum': 'CpuS390State',
+  'prefix': 'S390_CPU_STATE',
+  'data': [ 'uninitialized', 'stopped', 'check-stop', 'operating', 'load' ] }
+
+##
+# @CpuInfoS390:
+#
+# Additional information about a virtual S390 CPU
+#
+# @cpu-state: the virtual CPU's state
+#
+# Since: 2.12
+##
+{ 'struct': 'CpuInfoS390', 'data': { 'cpu-state': 'CpuS390State' } }
+
+##
 # @query-cpus:
 #
 # Returns a list of information about each virtual CPU.
diff --git a/target/s390x/cpu.c b/target/s390x/cpu.c
index da7cb9c..52b74ed 100644
--- a/target/s390x/cpu.c
+++ b/target/s390x/cpu.c
@@ -58,8 +58,8 @@ static bool s390_cpu_has_work(CPUState *cs)
     S390CPU *cpu = S390_CPU(cs);
 
     /* STOPPED cpus can never wake up */
-    if (s390_cpu_get_state(cpu) != CPU_STATE_LOAD &&
-        s390_cpu_get_state(cpu) != CPU_STATE_OPERATING) {
+    if (s390_cpu_get_state(cpu) != S390_CPU_STATE_LOAD &&
+        s390_cpu_get_state(cpu) != S390_CPU_STATE_OPERATING) {
         return false;
     }
 
@@ -77,7 +77,7 @@ static void s390_cpu_load_normal(CPUState *s)
     S390CPU *cpu = S390_CPU(s);
     cpu->env.psw.addr = ldl_phys(s->as, 4) & PSW_MASK_ESA_ADDR;
     cpu->env.psw.mask = PSW_MASK_32 | PSW_MASK_64;
-    s390_cpu_set_state(CPU_STATE_OPERATING, cpu);
+    s390_cpu_set_state(S390_CPU_STATE_OPERATING, cpu);
 }
 #endif
 
@@ -92,7 +92,7 @@ static void s390_cpu_reset(CPUState *s)
     env->bpbc = false;
     scc->parent_reset(s);
     cpu->env.sigp_order = 0;
-    s390_cpu_set_state(CPU_STATE_STOPPED, cpu);
+    s390_cpu_set_state(S390_CPU_STATE_STOPPED, cpu);
 }
 
 /* S390CPUClass::initial_reset() */
@@ -135,7 +135,7 @@ static void s390_cpu_full_reset(CPUState *s)
 
     scc->parent_reset(s);
     cpu->env.sigp_order = 0;
-    s390_cpu_set_state(CPU_STATE_STOPPED, cpu);
+    s390_cpu_set_state(S390_CPU_STATE_STOPPED, cpu);
 
     memset(env, 0, offsetof(CPUS390XState, end_reset_fields));
 
@@ -247,7 +247,7 @@ static void s390_cpu_initfn(Object *obj)
     env->tod_basetime = 0;
     env->tod_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, s390x_tod_timer, cpu);
     env->cpu_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, s390x_cpu_timer, cpu);
-    s390_cpu_set_state(CPU_STATE_STOPPED, cpu);
+    s390_cpu_set_state(S390_CPU_STATE_STOPPED, cpu);
 #endif
 }
 
@@ -275,8 +275,8 @@ static unsigned s390_count_running_cpus(void)
 
     CPU_FOREACH(cpu) {
         uint8_t state = S390_CPU(cpu)->env.cpu_state;
-        if (state == CPU_STATE_OPERATING ||
-            state == CPU_STATE_LOAD) {
+        if (state == S390_CPU_STATE_OPERATING ||
+            state == S390_CPU_STATE_LOAD) {
             if (!disabled_wait(cpu)) {
                 nr_running++;
             }
@@ -315,13 +315,13 @@ unsigned int s390_cpu_set_state(uint8_t cpu_state, S390CPU *cpu)
     trace_cpu_set_state(CPU(cpu)->cpu_index, cpu_state);
 
     switch (cpu_state) {
-    case CPU_STATE_STOPPED:
-    case CPU_STATE_CHECK_STOP:
+    case S390_CPU_STATE_STOPPED:
+    case S390_CPU_STATE_CHECK_STOP:
         /* halt the cpu for common infrastructure */
         s390_cpu_halt(cpu);
         break;
-    case CPU_STATE_OPERATING:
-    case CPU_STATE_LOAD:
+    case S390_CPU_STATE_OPERATING:
+    case S390_CPU_STATE_LOAD:
         /*
          * Starting a CPU with a PSW WAIT bit set:
          * KVM: handles this internally and triggers another WAIT exit.
diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
index 21ce40d..66baa7a 100644
--- a/target/s390x/cpu.h
+++ b/target/s390x/cpu.h
@@ -141,12 +141,9 @@ struct CPUS390XState {
      * architectures, there is a difference between a halt and a stop on s390.
      * If all cpus are either stopped (including check stop) or in the disabled
      * wait state, the vm can be shut down.
+     * The acceptable cpu_state values are defined in the CpuInfoS390State
+     * enum.
      */
-#define CPU_STATE_UNINITIALIZED        0x00
-#define CPU_STATE_STOPPED              0x01
-#define CPU_STATE_CHECK_STOP           0x02
-#define CPU_STATE_OPERATING            0x03
-#define CPU_STATE_LOAD                 0x04
     uint8_t cpu_state;
 
     /* currently processed sigp order */
diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
index 0301e9d..45dd1c5 100644
--- a/target/s390x/kvm.c
+++ b/target/s390x/kvm.c
@@ -1881,16 +1881,16 @@ int kvm_s390_set_cpu_state(S390CPU *cpu, uint8_t cpu_state)
     }
 
     switch (cpu_state) {
-    case CPU_STATE_STOPPED:
+    case S390_CPU_STATE_STOPPED:
         mp_state.mp_state = KVM_MP_STATE_STOPPED;
         break;
-    case CPU_STATE_CHECK_STOP:
+    case S390_CPU_STATE_CHECK_STOP:
         mp_state.mp_state = KVM_MP_STATE_CHECK_STOP;
         break;
-    case CPU_STATE_OPERATING:
+    case S390_CPU_STATE_OPERATING:
         mp_state.mp_state = KVM_MP_STATE_OPERATING;
         break;
-    case CPU_STATE_LOAD:
+    case S390_CPU_STATE_LOAD:
         mp_state.mp_state = KVM_MP_STATE_LOAD;
         break;
     default:
diff --git a/target/s390x/sigp.c b/target/s390x/sigp.c
index ac3f8e7..5a7a9c4 100644
--- a/target/s390x/sigp.c
+++ b/target/s390x/sigp.c
@@ -46,13 +46,13 @@ static void sigp_sense(S390CPU *dst_cpu, SigpInfo *si)
     }
 
     /* sensing without locks is racy, but it's the same for real hw */
-    if (state != CPU_STATE_STOPPED && !ext_call) {
+    if (state != S390_CPU_STATE_STOPPED && !ext_call) {
         si->cc = SIGP_CC_ORDER_CODE_ACCEPTED;
     } else {
         if (ext_call) {
             status |= SIGP_STAT_EXT_CALL_PENDING;
         }
-        if (state == CPU_STATE_STOPPED) {
+        if (state == S390_CPU_STATE_STOPPED) {
             status |= SIGP_STAT_STOPPED;
         }
         set_sigp_status(si, status);
@@ -94,12 +94,12 @@ static void sigp_start(CPUState *cs, run_on_cpu_data arg)
     S390CPU *cpu = S390_CPU(cs);
     SigpInfo *si = arg.host_ptr;
 
-    if (s390_cpu_get_state(cpu) != CPU_STATE_STOPPED) {
+    if (s390_cpu_get_state(cpu) != S390_CPU_STATE_STOPPED) {
         si->cc = SIGP_CC_ORDER_CODE_ACCEPTED;
         return;
     }
 
-    s390_cpu_set_state(CPU_STATE_OPERATING, cpu);
+    s390_cpu_set_state(S390_CPU_STATE_OPERATING, cpu);
     si->cc = SIGP_CC_ORDER_CODE_ACCEPTED;
 }
 
@@ -108,14 +108,14 @@ static void sigp_stop(CPUState *cs, run_on_cpu_data arg)
     S390CPU *cpu = S390_CPU(cs);
     SigpInfo *si = arg.host_ptr;
 
-    if (s390_cpu_get_state(cpu) != CPU_STATE_OPERATING) {
+    if (s390_cpu_get_state(cpu) != S390_CPU_STATE_OPERATING) {
         si->cc = SIGP_CC_ORDER_CODE_ACCEPTED;
         return;
     }
 
     /* disabled wait - sleeping in user space */
     if (cs->halted) {
-        s390_cpu_set_state(CPU_STATE_STOPPED, cpu);
+        s390_cpu_set_state(S390_CPU_STATE_STOPPED, cpu);
     } else {
         /* execute the stop function */
         cpu->env.sigp_order = SIGP_STOP;
@@ -130,17 +130,17 @@ static void sigp_stop_and_store_status(CPUState *cs, run_on_cpu_data arg)
     SigpInfo *si = arg.host_ptr;
 
     /* disabled wait - sleeping in user space */
-    if (s390_cpu_get_state(cpu) == CPU_STATE_OPERATING && cs->halted) {
-        s390_cpu_set_state(CPU_STATE_STOPPED, cpu);
+    if (s390_cpu_get_state(cpu) == S390_CPU_STATE_OPERATING && cs->halted) {
+        s390_cpu_set_state(S390_CPU_STATE_STOPPED, cpu);
     }
 
     switch (s390_cpu_get_state(cpu)) {
-    case CPU_STATE_OPERATING:
+    case S390_CPU_STATE_OPERATING:
         cpu->env.sigp_order = SIGP_STOP_STORE_STATUS;
         cpu_inject_stop(cpu);
         /* store will be performed in do_stop_interrup() */
         break;
-    case CPU_STATE_STOPPED:
+    case S390_CPU_STATE_STOPPED:
         /* already stopped, just store the status */
         cpu_synchronize_state(cs);
         s390_store_status(cpu, S390_STORE_STATUS_DEF_ADDR, true);
@@ -156,7 +156,7 @@ static void sigp_store_status_at_address(CPUState *cs, run_on_cpu_data arg)
     uint32_t address = si->param & 0x7ffffe00u;
 
     /* cpu has to be stopped */
-    if (s390_cpu_get_state(cpu) != CPU_STATE_STOPPED) {
+    if (s390_cpu_get_state(cpu) != S390_CPU_STATE_STOPPED) {
         set_sigp_status(si, SIGP_STAT_INCORRECT_STATE);
         return;
     }
@@ -186,7 +186,7 @@ static void sigp_store_adtl_status(CPUState *cs, run_on_cpu_data arg)
     }
 
     /* cpu has to be stopped */
-    if (s390_cpu_get_state(cpu) != CPU_STATE_STOPPED) {
+    if (s390_cpu_get_state(cpu) != S390_CPU_STATE_STOPPED) {
         set_sigp_status(si, SIGP_STAT_INCORRECT_STATE);
         return;
     }
@@ -229,17 +229,17 @@ static void sigp_restart(CPUState *cs, run_on_cpu_data arg)
     SigpInfo *si = arg.host_ptr;
 
     switch (s390_cpu_get_state(cpu)) {
-    case CPU_STATE_STOPPED:
+    case S390_CPU_STATE_STOPPED:
         /* the restart irq has to be delivered prior to any other pending irq */
         cpu_synchronize_state(cs);
         /*
          * Set OPERATING (and unhalting) before loading the restart PSW.
          * load_psw() will then properly halt the CPU again if necessary (TCG).
          */
-        s390_cpu_set_state(CPU_STATE_OPERATING, cpu);
+        s390_cpu_set_state(S390_CPU_STATE_OPERATING, cpu);
         do_restart_interrupt(&cpu->env);
         break;
-    case CPU_STATE_OPERATING:
+    case S390_CPU_STATE_OPERATING:
         cpu_inject_restart(cpu);
         break;
     }
@@ -285,7 +285,7 @@ static void sigp_set_prefix(CPUState *cs, run_on_cpu_data arg)
     }
 
     /* cpu has to be stopped */
-    if (s390_cpu_get_state(cpu) != CPU_STATE_STOPPED) {
+    if (s390_cpu_get_state(cpu) != S390_CPU_STATE_STOPPED) {
         set_sigp_status(si, SIGP_STAT_INCORRECT_STATE);
         return;
     }
@@ -318,7 +318,7 @@ static void sigp_cond_emergency(S390CPU *src_cpu, S390CPU *dst_cpu,
     p_asn = dst_cpu->env.cregs[4] & 0xffff;  /* Primary ASN */
     s_asn = dst_cpu->env.cregs[3] & 0xffff;  /* Secondary ASN */
 
-    if (s390_cpu_get_state(dst_cpu) != CPU_STATE_STOPPED ||
+    if (s390_cpu_get_state(dst_cpu) != S390_CPU_STATE_STOPPED ||
         (psw_mask & psw_int_mask) != psw_int_mask ||
         (idle && psw_addr != 0) ||
         (!idle && (asn == p_asn || asn == s_asn))) {
@@ -435,7 +435,7 @@ static int sigp_set_architecture(S390CPU *cpu, uint32_t param,
         if (cur_cpu == cpu) {
             continue;
         }
-        if (s390_cpu_get_state(cur_cpu) != CPU_STATE_STOPPED) {
+        if (s390_cpu_get_state(cur_cpu) != S390_CPU_STATE_STOPPED) {
             all_stopped = false;
         }
     }
@@ -492,7 +492,7 @@ void do_stop_interrupt(CPUS390XState *env)
 {
     S390CPU *cpu = s390_env_get_cpu(env);
 
-    if (s390_cpu_set_state(CPU_STATE_STOPPED, cpu) == 0) {
+    if (s390_cpu_set_state(S390_CPU_STATE_STOPPED, cpu) == 0) {
         qemu_system_shutdown_request(SHUTDOWN_CAUSE_GUEST_SHUTDOWN);
     }
     if (cpu->env.sigp_order == SIGP_STOP_STORE_STATUS) {
-- 
1.9.1

[Qemu-devel] [PATCHv3 2/4] qmp: add query-cpus-fast

[Viktor Mihajlovski]

From: Luiz Capitulino <lcapitulino@redhat.com>

The query-cpus command has an extremely serious side effect:
it always interrupts all running vCPUs so that they can run
ioctl calls. This can cause a huge performance degradation for
some workloads. And most of the information retrieved by the
ioctl calls are not even used by query-cpus.

This commit introduces a replacement for query-cpus called
query-cpus-fast, which has the following features:

 o Never interrupt vCPUs threads. query-cpus-fast only returns
   vCPU information maintained by QEMU itself, which should be
   sufficient for most management software needs

 o Drop "halted" field as it can not retrieved in a fast
   way on most architectures

 o Drop irrelevant fields such as "current", "pc" and "arch"

 o Rename some fields for better clarification & proper naming
   standard

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Acked-by: Eric Blake <eblake@redhat.com>
---
 cpus.c               | 38 ++++++++++++++++++++++++++++
 hmp-commands-info.hx | 14 +++++++++++
 hmp.c                | 14 +++++++++++
 hmp.h                |  1 +
 qapi-schema.json     | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 137 insertions(+)

diff --git a/cpus.c b/cpus.c
index 6006931..6df6660 100644
--- a/cpus.c
+++ b/cpus.c
@@ -2156,6 +2156,44 @@ CpuInfoList *qmp_query_cpus(Error **errp)
     return head;
 }
 
+/*
+ * fast means: we NEVER interrupt vCPU threads to retrieve
+ * information from KVM.
+ */
+CpuInfoFastList *qmp_query_cpus_fast(Error **errp)
+{
+    MachineState *ms = MACHINE(qdev_get_machine());
+    MachineClass *mc = MACHINE_GET_CLASS(ms);
+    CpuInfoFastList *head = NULL, *cur_item = NULL;
+    CPUState *cpu;
+
+    CPU_FOREACH(cpu) {
+        CpuInfoFastList *info = g_malloc0(sizeof(*info));
+        info->value = g_malloc0(sizeof(*info->value));
+
+        info->value->cpu_index = cpu->cpu_index;
+        info->value->qom_path = object_get_canonical_path(OBJECT(cpu));
+        info->value->thread_id = cpu->thread_id;
+
+        info->value->has_props = !!mc->cpu_index_to_instance_props;
+        if (info->value->has_props) {
+            CpuInstanceProperties *props;
+            props = g_malloc0(sizeof(*props));
+            *props = mc->cpu_index_to_instance_props(ms, cpu->cpu_index);
+            info->value->props = props;
+        }
+
+        if (!cur_item) {
+            head = cur_item = info;
+        } else {
+            cur_item->next = info;
+            cur_item = info;
+        }
+    }
+
+    return head;
+}
+
 void qmp_memsave(int64_t addr, int64_t size, const char *filename,
                  bool has_cpu, int64_t cpu_index, Error **errp)
 {
diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
index ad590a4..16ac602 100644
--- a/hmp-commands-info.hx
+++ b/hmp-commands-info.hx
@@ -160,6 +160,20 @@ Show infos for each CPU.
 ETEXI
 
     {
+        .name       = "cpus_fast",
+        .args_type  = "",
+        .params     = "",
+        .help       = "show information for each CPU without interrupting them",
+        .cmd        = hmp_info_cpus_fast,
+    },
+
+STEXI
+@item info cpus_fast
+@findex info cpus_fast
+Show infos for each CPU without performance penalty.
+ETEXI
+
+    {
         .name       = "history",
         .args_type  = "",
         .params     = "",
diff --git a/hmp.c b/hmp.c
index a6b94b7..0bd3b3a 100644
--- a/hmp.c
+++ b/hmp.c
@@ -410,6 +410,20 @@ void hmp_info_cpus(Monitor *mon, const QDict *qdict)
     qapi_free_CpuInfoList(cpu_list);
 }
 
+void hmp_info_cpus_fast(Monitor *mon, const QDict *qdict)
+{
+    CpuInfoFastList *head, *cpu;
+
+    head = qmp_query_cpus_fast(NULL);
+
+    for (cpu = head; cpu; cpu = cpu->next) {
+        monitor_printf(mon, "  CPU #%" PRId64 ":", cpu->value->cpu_index);
+        monitor_printf(mon, " thread-id=%" PRId64 "\n", cpu->value->thread_id);
+    }
+
+    qapi_free_CpuInfoFastList(head);
+}
+
 static void print_block_info(Monitor *mon, BlockInfo *info,
                              BlockDeviceInfo *inserted, bool verbose)
 {
diff --git a/hmp.h b/hmp.h
index 1143db4..93fb4e4 100644
--- a/hmp.h
+++ b/hmp.h
@@ -29,6 +29,7 @@ void hmp_info_migrate_capabilities(Monitor *mon, const QDict *qdict);
 void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict);
 void hmp_info_migrate_cache_size(Monitor *mon, const QDict *qdict);
 void hmp_info_cpus(Monitor *mon, const QDict *qdict);
+void hmp_info_cpus_fast(Monitor *mon, const QDict *qdict);
 void hmp_info_block(Monitor *mon, const QDict *qdict);
 void hmp_info_blockstats(Monitor *mon, const QDict *qdict);
 void hmp_info_vnc(Monitor *mon, const QDict *qdict);
diff --git a/qapi-schema.json b/qapi-schema.json
index 94d560e..815f072 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -552,6 +552,12 @@
 #
 # Returns a list of information about each virtual CPU.
 #
+# This command causes vCPU threads to exit to userspace, which causes
+# a small interruption to guest CPU execution. This will have a negative
+# impact on realtime guests and other latency sensitive guest workloads.
+# It is recommended to use @query-cpus-fast instead of this command to
+# avoid the vCPU interruption.
+#
 # Returns: a list of @CpuInfo for each virtual CPU
 #
 # Since: 0.14.0
@@ -585,6 +591,70 @@
 { 'command': 'query-cpus', 'returns': ['CpuInfo'] }
 
 ##
+# @CpuInfoFast:
+#
+# Information about a virtual CPU
+#
+# @cpu-index: index of the virtual CPU
+#
+# @qom-path: path to the CPU object in the QOM tree
+#
+# @thread-id: ID of the underlying host thread
+#
+# @props: properties describing to which node/socket/core/thread
+#         virtual CPU belongs to, provided if supported by board
+#
+# Since: 2.12
+#
+##
+{ 'struct': 'CpuInfoFast',
+  'data': {'cpu-index': 'int', 'qom-path': 'str',
+           'thread-id': 'int', '*props': 'CpuInstanceProperties' } }
+
+##
+# @query-cpus-fast:
+#
+# Returns information about all virtual CPUs. This command does not
+# incur a performance penalty and should be used in production
+# instead of query-cpus.
+#
+# Returns: list of @CpuInfoFast
+#
+# Notes: The CPU architecture name is not returned by query-cpus-fast.
+#        Use query-target to retrieve that information.
+#
+# Since: 2.12
+#
+# Example:
+#
+# -> { "execute": "query-cpus-fast" }
+# <- { "return": [
+#         {
+#             "thread-id": 25627,
+#             "props": {
+#                 "core-id": 0,
+#                 "thread-id": 0,
+#                 "socket-id": 0
+#             },
+#             "qom-path": "/machine/unattached/device[0]",
+#             "cpu-index": 0
+#         },
+#         {
+#             "thread-id": 25628,
+#             "props": {
+#                 "core-id": 0,
+#                 "thread-id": 0,
+#                 "socket-id": 1
+#             },
+#             "qom-path": "/machine/unattached/device[2]",
+#             "cpu-index": 1
+#         }
+#     ]
+# }
+##
+{ 'command': 'query-cpus-fast', 'returns': [ 'CpuInfoFast' ] }
+
+##
 # @IOThreadInfo:
 #
 # Information about an iothread
-- 
1.9.1

[Qemu-devel] [PATCHv3 3/4] qmp: add architecture specific cpu data for query-cpus-fast

[Viktor Mihajlovski]

The s390 CPU state can be retrieved without interrupting the
VM execution. Extendend the CpuInfoFast union with architecture
specific data and an implementation for s390.

Return data looks like this:
 [
   {"thread-id":64301,"props":{"core-id":0},
    "arch":"s390","cpu-state":"operating",
    "qom-path":"/machine/unattached/device[0]","cpu-index":0},
   {"thread-id":64302,"props":{"core-id":1},
    "arch":"s390","cpu-state":"operating",
    "qom-path":"/machine/unattached/device[1]","cpu-index":1}
]

Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Acked-by: Eric Blake <eblake@redhat.com>
---
 cpus.c           | 10 ++++++++++
 hmp.c            | 10 ++++++++++
 qapi-schema.json | 25 ++++++++++++++++++-------
 3 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/cpus.c b/cpus.c
index 6df6660..af67826 100644
--- a/cpus.c
+++ b/cpus.c
@@ -2166,6 +2166,10 @@ CpuInfoFastList *qmp_query_cpus_fast(Error **errp)
     MachineClass *mc = MACHINE_GET_CLASS(ms);
     CpuInfoFastList *head = NULL, *cur_item = NULL;
     CPUState *cpu;
+#if defined(TARGET_S390X)
+    S390CPU *s390_cpu;
+    CPUS390XState *env;
+#endif
 
     CPU_FOREACH(cpu) {
         CpuInfoFastList *info = g_malloc0(sizeof(*info));
@@ -2183,6 +2187,12 @@ CpuInfoFastList *qmp_query_cpus_fast(Error **errp)
             info->value->props = props;
         }
 
+#if defined(TARGET_S390X)
+        s390_cpu = S390_CPU(cpu);
+        env = &s390_cpu->env;
+        info->value->arch = CPU_INFO_ARCH_S390;
+        info->value->u.s390.cpu_state = env->cpu_state;
+#endif
         if (!cur_item) {
             head = cur_item = info;
         } else {
diff --git a/hmp.c b/hmp.c
index 0bd3b3a..e27433e 100644
--- a/hmp.c
+++ b/hmp.c
@@ -418,6 +418,16 @@ void hmp_info_cpus_fast(Monitor *mon, const QDict *qdict)
 
     for (cpu = head; cpu; cpu = cpu->next) {
         monitor_printf(mon, "  CPU #%" PRId64 ":", cpu->value->cpu_index);
+
+        switch (cpu->value->arch) {
+        case CPU_INFO_ARCH_S390:
+            monitor_printf(mon, " state=%s",
+                           CpuS390State_str(cpu->value->u.s390.cpu_state));
+            break;
+        default:
+            break;
+        }
+
         monitor_printf(mon, " thread-id=%" PRId64 "\n", cpu->value->thread_id);
     }
 
diff --git a/qapi-schema.json b/qapi-schema.json
index 815f072..e6ca63f 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -408,7 +408,7 @@
 # @CpuInfoArch:
 #
 # An enumeration of cpu types that enable additional information during
-# @query-cpus.
+# @query-cpus and @query-cpus-fast.
 #
 # @s390: since 2.12
 #
@@ -604,12 +604,24 @@
 # @props: properties describing to which node/socket/core/thread
 #         virtual CPU belongs to, provided if supported by board
 #
+# @arch: architecture of the cpu, which determines which additional fields
+#        will be listed
+#
 # Since: 2.12
 #
 ##
-{ 'struct': 'CpuInfoFast',
-  'data': {'cpu-index': 'int', 'qom-path': 'str',
-           'thread-id': 'int', '*props': 'CpuInstanceProperties' } }
+{ 'union': 'CpuInfoFast',
+  'base': {'cpu-index': 'int', 'qom-path': 'str',
+           'thread-id': 'int', '*props': 'CpuInstanceProperties',
+           'arch': 'CpuInfoArch' },
+  'discriminator': 'arch',
+  'data': { 'x86': 'CpuInfoOther',
+            'sparc': 'CpuInfoOther',
+            'ppc': 'CpuInfoOther',
+            'mips': 'CpuInfoOther',
+            'tricore': 'CpuInfoOther',
+            's390': 'CpuInfoS390',
+            'other': 'CpuInfoOther' } }
 
 ##
 # @query-cpus-fast:
@@ -620,9 +632,6 @@
 #
 # Returns: list of @CpuInfoFast
 #
-# Notes: The CPU architecture name is not returned by query-cpus-fast.
-#        Use query-target to retrieve that information.
-#
 # Since: 2.12
 #
 # Example:
@@ -637,6 +646,7 @@
 #                 "socket-id": 0
 #             },
 #             "qom-path": "/machine/unattached/device[0]",
+#             "arch":"x86",
 #             "cpu-index": 0
 #         },
 #         {
@@ -647,6 +657,7 @@
 #                 "socket-id": 1
 #             },
 #             "qom-path": "/machine/unattached/device[2]",
+#             "arch":"x86",
 #             "cpu-index": 1
 #         }
 #     ]
-- 
1.9.1

[Qemu-devel] [PATCHv3 4/4] qemu-doc: deprecate query-cpus and info cpus

[Viktor Mihajlovski]

Start the deprecation period for QAPI query-cpus (replaced by
query-cpus-fast) and HMP 'info cpus' (replaced by 'info cpus_fast')
beginning with 2.12.0.

Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
---
 hmp-commands-info.hx |  4 ++--
 qapi-schema.json     |  4 ++++
 qemu-doc.texi        | 10 ++++++++++
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
index 16ac602..2ccb9c7 100644
--- a/hmp-commands-info.hx
+++ b/hmp-commands-info.hx
@@ -149,14 +149,14 @@ ETEXI
         .name       = "cpus",
         .args_type  = "",
         .params     = "",
-        .help       = "show infos for each CPU",
+        .help       = "show infos for each CPU (deprecated, use info cpus_fast instead)",
         .cmd        = hmp_info_cpus,
     },
 
 STEXI
 @item info cpus
 @findex info cpus
-Show infos for each CPU.
+Show infos for each CPU. Deprecated, please use @code{info cpus_fast} instead.
 ETEXI
 
     {
diff --git a/qapi-schema.json b/qapi-schema.json
index e6ca63f..cd98a94 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -587,6 +587,10 @@
 #       ]
 #    }
 #
+# Notes: This interface is deprecated (since 2.12.0), and it is strongly
+#        recommended that you avoid using it. Use @query-cpus-fast to
+#        obtain information about virtual CPUs.
+#
 ##
 { 'command': 'query-cpus', 'returns': ['CpuInfo'] }
 
diff --git a/qemu-doc.texi b/qemu-doc.texi
index 769968a..46aacb6 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -2757,6 +2757,12 @@ used and it will be removed with no replacement.
 The ``convert -s snapshot_id_or_name'' argument is obsoleted
 by the ``convert -l snapshot_param'' argument instead.
 
+@section System emulator monitor commands
+
+@subsection query-cpus (since 2.12.0)
+
+The ``query-cpus'' command is replaced by the ``query-cpus-fast'' command.
+
 @section System emulator human monitor commands
 
 @subsection host_net_add (since 2.10.0)
@@ -2767,6 +2773,10 @@ The ``host_net_add'' command is replaced by the ``netdev_add'' command.
 
 The ``host_net_remove'' command is replaced by the ``netdev_del'' command.
 
+@subsection info cpus (since 2.12.0)
+
+The ``info cpus'' command is replaced by the ``info cpus_fast'' command.
+
 @section System emulator devices
 
 @subsection ivshmem (since 2.6.0)
-- 
1.9.1

Re: [Qemu-devel] [PATCHv3 2/4] qmp: add query-cpus-fast

[Eric Blake]

On 02/15/2018 04:20 AM, Viktor Mihajlovski wrote:
> From: Luiz Capitulino <lcapitulino@redhat.com>
> 
> The query-cpus command has an extremely serious side effect:
> it always interrupts all running vCPUs so that they can run
> ioctl calls. This can cause a huge performance degradation for
> some workloads. And most of the information retrieved by the
> ioctl calls are not even used by query-cpus.
> 
> This commit introduces a replacement for query-cpus called
> query-cpus-fast, which has the following features:
> 
>   o Never interrupt vCPUs threads. query-cpus-fast only returns
>     vCPU information maintained by QEMU itself, which should be
>     sufficient for most management software needs
> 
>   o Drop "halted" field as it can not retrieved in a fast

s/can not retrieved/cannot be retrieved/

>     way on most architectures
> 
>   o Drop irrelevant fields such as "current", "pc" and "arch"
> 
>   o Rename some fields for better clarification & proper naming
>     standard
> 
> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Acked-by: Eric Blake <eblake@redhat.com>
> ---

> +++ b/hmp-commands-info.hx
> @@ -160,6 +160,20 @@ Show infos for each CPU.

Pre-existing, but while we are here, it wouldn't hurt to do 
s/infos/information/

>   ETEXI
>   
>       {
> +        .name       = "cpus_fast",
> +        .args_type  = "",
> +        .params     = "",
> +        .help       = "show information for each CPU without interrupting them",
> +        .cmd        = hmp_info_cpus_fast,
> +    },
> +
> +STEXI
> +@item info cpus_fast
> +@findex info cpus_fast
> +Show infos for each CPU without performance penalty.

and again here, where you copied and pasted.

You know, we have no back-compat guarantees on HMP.  We could make 'info 
cpu' just ALWAYS call query-cpus-fast, with no HMP counterpart for the 
slower query-cpus, and without needing a deprecation period.  But I'll 
leave that up to David if that makes more sense.

> +++ b/hmp.c
> @@ -410,6 +410,20 @@ void hmp_info_cpus(Monitor *mon, const QDict *qdict)
>       qapi_free_CpuInfoList(cpu_list);
>   }
>   
> +void hmp_info_cpus_fast(Monitor *mon, const QDict *qdict)
> +{
> +    CpuInfoFastList *head, *cpu;
> +
> +    head = qmp_query_cpus_fast(NULL);
> +
> +    for (cpu = head; cpu; cpu = cpu->next) {
> +        monitor_printf(mon, "  CPU #%" PRId64 ":", cpu->value->cpu_index);
> +        monitor_printf(mon, " thread-id=%" PRId64 "\n", cpu->value->thread_id);
> +    }

This is particularly true since your HMP implementation is not even 
printing all the information returned by query-cpus-fast!

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [Qemu-devel] [PATCHv3 4/4] qemu-doc: deprecate query-cpus and info cpus

[Eric Blake]

On 02/15/2018 04:20 AM, Viktor Mihajlovski wrote:
> Start the deprecation period for QAPI query-cpus (replaced by
> query-cpus-fast) and HMP 'info cpus' (replaced by 'info cpus_fast')
> beginning with 2.12.0.

See my comments on 2/4 - if we want, we could just make HMP 'info cpus' 
be the fast version, with no slow version counterpart, right away 
without a deprecation period.  If we do that, then...

> 
> Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
> ---
>   hmp-commands-info.hx |  4 ++--
>   qapi-schema.json     |  4 ++++
>   qemu-doc.texi        | 10 ++++++++++
>   3 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
> index 16ac602..2ccb9c7 100644
> --- a/hmp-commands-info.hx
> +++ b/hmp-commands-info.hx
> @@ -149,14 +149,14 @@ ETEXI
>           .name       = "cpus",
>           .args_type  = "",
>           .params     = "",
> -        .help       = "show infos for each CPU",
> +        .help       = "show infos for each CPU (deprecated, use info cpus_fast instead)",

changes to this file no longer need to happen in this patch, and


> +++ b/qemu-doc.texi
> @@ -2757,6 +2757,12 @@ used and it will be removed with no replacement.
>   The ``convert -s snapshot_id_or_name'' argument is obsoleted
>   by the ``convert -l snapshot_param'' argument instead.
>   
> +@section System emulator monitor commands
> +
> +@subsection query-cpus (since 2.12.0)
> +
> +The ``query-cpus'' command is replaced by the ``query-cpus-fast'' command.
> +
>   @section System emulator human monitor commands
>   
>   @subsection host_net_add (since 2.10.0)
> @@ -2767,6 +2773,10 @@ The ``host_net_add'' command is replaced by the ``netdev_add'' command.
>   
>   The ``host_net_remove'' command is replaced by the ``netdev_del'' command.
>   
> +@subsection info cpus (since 2.12.0)
> +
> +The ``info cpus'' command is replaced by the ``info cpus_fast'' command.
> +

this hunk could be dropped.

But if we really want a deprecation period on the HMP side as well, then 
this patch is fine.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [Qemu-devel] [PATCHv3 2/4] qmp: add query-cpus-fast

[Viktor Mihajlovski]

On 15.02.2018 15:19, Eric Blake wrote:
> On 02/15/2018 04:20 AM, Viktor Mihajlovski wrote:
>> From: Luiz Capitulino <lcapitulino@redhat.com>
>>
>> The query-cpus command has an extremely serious side effect:
>> it always interrupts all running vCPUs so that they can run
>> ioctl calls. This can cause a huge performance degradation for
>> some workloads. And most of the information retrieved by the
>> ioctl calls are not even used by query-cpus.
>>
>> This commit introduces a replacement for query-cpus called
>> query-cpus-fast, which has the following features:
>>
>>   o Never interrupt vCPUs threads. query-cpus-fast only returns
>>     vCPU information maintained by QEMU itself, which should be
>>     sufficient for most management software needs
>>
>>   o Drop "halted" field as it can not retrieved in a fast
> 
> s/can not retrieved/cannot be retrieved/
> 
>>     way on most architectures
>>
>>   o Drop irrelevant fields such as "current", "pc" and "arch"
>>
>>   o Rename some fields for better clarification & proper naming
>>     standard
>>
>> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
>> Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>> Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>> Acked-by: Eric Blake <eblake@redhat.com>
>> ---
> 
>> +++ b/hmp-commands-info.hx
>> @@ -160,6 +160,20 @@ Show infos for each CPU.
> 
> Pre-existing, but while we are here, it wouldn't hurt to do
> s/infos/information/
> 
>>   ETEXI
>>         {
>> +        .name       = "cpus_fast",
>> +        .args_type  = "",
>> +        .params     = "",
>> +        .help       = "show information for each CPU without
>> interrupting them",
>> +        .cmd        = hmp_info_cpus_fast,
>> +    },
>> +
>> +STEXI
>> +@item info cpus_fast
>> +@findex info cpus_fast
>> +Show infos for each CPU without performance penalty.
> 
> and again here, where you copied and pasted.
> 
> You know, we have no back-compat guarantees on HMP.  We could make 'info
> cpu' just ALWAYS call query-cpus-fast, with no HMP counterpart for the
> slower query-cpus, and without needing a deprecation period.  But I'll
> leave that up to David if that makes more sense.
Ditching info cpus_fast would make me happy as well, because it would
cause less headache on the libvirt side of things.
> 
>> +++ b/hmp.c
>> @@ -410,6 +410,20 @@ void hmp_info_cpus(Monitor *mon, const QDict *qdict)
>>       qapi_free_CpuInfoList(cpu_list);
>>   }
>>   +void hmp_info_cpus_fast(Monitor *mon, const QDict *qdict)
>> +{
>> +    CpuInfoFastList *head, *cpu;
>> +
>> +    head = qmp_query_cpus_fast(NULL);
>> +
>> +    for (cpu = head; cpu; cpu = cpu->next) {
>> +        monitor_printf(mon, "  CPU #%" PRId64 ":",
>> cpu->value->cpu_index);
>> +        monitor_printf(mon, " thread-id=%" PRId64 "\n",
>> cpu->value->thread_id);
>> +    }
> 
> This is particularly true since your HMP implementation is not even
> printing all the information returned by query-cpus-fast!
> 


-- 
Regards,
 Viktor Mihajlovski

Re: [Qemu-devel] [PATCHv3 2/4] qmp: add query-cpus-fast

[Eric Blake]

On 02/15/2018 08:40 AM, Viktor Mihajlovski wrote:
> On 15.02.2018 15:19, Eric Blake wrote:
>> On 02/15/2018 04:20 AM, Viktor Mihajlovski wrote:
>>> From: Luiz Capitulino <lcapitulino@redhat.com>
>>>
>>> The query-cpus command has an extremely serious side effect:
>>> it always interrupts all running vCPUs so that they can run
>>> ioctl calls. This can cause a huge performance degradation for
>>> some workloads. And most of the information retrieved by the
>>> ioctl calls are not even used by query-cpus.
>>>
>>> This commit introduces a replacement for query-cpus called

>> You know, we have no back-compat guarantees on HMP.  We could make 'info
>> cpu' just ALWAYS call query-cpus-fast, with no HMP counterpart for the
>> slower query-cpus, and without needing a deprecation period.  But I'll
>> leave that up to David if that makes more sense.
> Ditching info cpus_fast would make me happy as well, because it would
> cause less headache on the libvirt side of things.

Why is libvirt using HMP in the first place?  Libvirt should always be 
using the QMP command, when one exists.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [Qemu-devel] [PATCHv3 2/4] qmp: add query-cpus-fast

[Viktor Mihajlovski]

On 15.02.2018 15:53, Eric Blake wrote:
> On 02/15/2018 08:40 AM, Viktor Mihajlovski wrote:
>> On 15.02.2018 15:19, Eric Blake wrote:
>>> On 02/15/2018 04:20 AM, Viktor Mihajlovski wrote:
>>>> From: Luiz Capitulino <lcapitulino@redhat.com>
>>>>
>>>> The query-cpus command has an extremely serious side effect:
>>>> it always interrupts all running vCPUs so that they can run
>>>> ioctl calls. This can cause a huge performance degradation for
>>>> some workloads. And most of the information retrieved by the
>>>> ioctl calls are not even used by query-cpus.
>>>>
>>>> This commit introduces a replacement for query-cpus called
> 
>>> You know, we have no back-compat guarantees on HMP.  We could make 'info
>>> cpu' just ALWAYS call query-cpus-fast, with no HMP counterpart for the
>>> slower query-cpus, and without needing a deprecation period.  But I'll
>>> leave that up to David if that makes more sense.
>> Ditching info cpus_fast would make me happy as well, because it would
>> cause less headache on the libvirt side of things.
> 
> Why is libvirt using HMP in the first place?  Libvirt should always be
> using the QMP command, when one exists.
> Which it does, but there's still a lot of fallback code including HMP
"info cpus". In real life this should of course never be used, because
the QMP is always there.

-- 
Regards,
 Viktor Mihajlovski