[PATCH v4 1/1] monitor: Support specified vCPU registers

[zhenwei pi]

Originally we have to get all the vCPU registers and parse the
specified one. To improve the performance of this usage, allow user
specified vCPU id to query registers.

Run a VM with 16 vCPU, use bcc tool to track the latency of
'hmp_info_registers':
'info registers -a' uses about 3ms;
'info registers 12' uses about 150us.

Cc: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
---
 hmp-commands-info.hx |  8 +++++---
 monitor/misc.c       | 10 ++++++++--
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
index 188d9ece3b..e012035541 100644
--- a/hmp-commands-info.hx
+++ b/hmp-commands-info.hx
@@ -100,9 +100,11 @@ ERST
 
     {
         .name       = "registers",
-        .args_type  = "cpustate_all:-a",
-        .params     = "[-a]",
-        .help       = "show the cpu registers (-a: all - show register info 
for all cpus)",
+        .args_type  = "cpustate_all:-a,vcpu:i?",
+        .params     = "[-a|vcpu]",
+        .help       = "show the cpu registers (-a: show register info for all 
cpus;"
+                      " vcpu: specific vCPU to query; show the current CPU's 
registers if"
+                      " no argument is specified)",
         .cmd        = hmp_info_registers,
     },
 
diff --git a/monitor/misc.c b/monitor/misc.c
index 3d2312ba8d..6436a8786b 100644
--- a/monitor/misc.c
+++ b/monitor/misc.c
@@ -307,6 +307,7 @@ int monitor_get_cpu_index(Monitor *mon)
 static void hmp_info_registers(Monitor *mon, const QDict *qdict)
 {
     bool all_cpus = qdict_get_try_bool(qdict, "cpustate_all", false);
+    int vcpu = qdict_get_try_int(qdict, "vcpu", -1);
     CPUState *cs;
 
     if (all_cpus) {
@@ -315,13 +316,18 @@ static void hmp_info_registers(Monitor *mon, const QDict 
*qdict)
             cpu_dump_state(cs, NULL, CPU_DUMP_FPU);
         }
     } else {
-        cs = mon_get_cpu(mon);
+        cs = vcpu >= 0 ? qemu_get_cpu(vcpu) : mon_get_cpu(mon);
 
         if (!cs) {
-            monitor_printf(mon, "No CPU available\n");
+            if (vcpu >= 0) {
+                monitor_printf(mon, "CPU#%d not available\n", vcpu);
+            } else {
+                monitor_printf(mon, "No CPU available\n");
+            }
             return;
         }
 
+        monitor_printf(mon, "\nCPU#%d\n", cs->cpu_index);
         cpu_dump_state(cs, NULL, CPU_DUMP_FPU);
     }
 }
-- 
2.20.1