[Xen-devel] [PATCH] reduce 'd' debug key's global impact

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

On large systems, dumping state may cause time management to get
stalled for so long a period that it wouldn't recover. Therefore alter
the state dumping logic to
- block each CPU as it prints rather than one CPU for a very long time
- don't print useless data (e.g. the hypervisor context of the
  interrupt that is used for triggering the printing, but isn't part
  of the context that's actuall interesting.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- 2010-05-04.orig/xen/arch/ia64/linux-xen/smp.c       2009-05-27 
13:54:05.000000000 +0200
+++ 2010-05-04/xen/arch/ia64/linux-xen/smp.c    2010-05-04 13:22:27.000000000 
+0200
@@ -189,7 +189,7 @@ handle_IPI (int irq, void *dev_id, struc
                                       * At this point the structure may be 
gone unless
                                       * wait is true.
                                       */
-                                     (*func)(info);
+                                     (*func)(info ?: regs);
 
                                      /* Notify the sending CPU that the task 
is done.  */
                                      mb();
--- 2010-05-04.orig/xen/arch/x86/smp.c  2010-04-22 14:43:25.000000000 +0200
+++ 2010-05-04/xen/arch/x86/smp.c       2010-05-04 13:22:27.000000000 +0200
@@ -395,7 +395,7 @@ static void __smp_call_function_interrup
 
     if ( call_data.wait )
     {
-        (*func)(info);
+        (*func)(info ?: get_irq_regs());
         mb();
         atomic_inc(&call_data.finished);
     }
@@ -403,7 +403,7 @@ static void __smp_call_function_interrup
     {
         mb();
         atomic_inc(&call_data.started);
-        (*func)(info);
+        (*func)(info ?: get_irq_regs());
     }
 
     irq_exit();
--- 2010-05-04.orig/xen/common/keyhandler.c     2010-05-04 13:21:53.000000000 
+0200
+++ 2010-05-04/xen/common/keyhandler.c  2010-05-04 13:22:27.000000000 +0200
@@ -71,20 +71,45 @@ static struct keyhandler show_handlers_k
     .desc = "show this message"
 };
 
-static void __dump_execstate(void *unused)
+static cpumask_t dump_execstate_mask;
+
+static void __dump_execstate(void *_regs)
 {
-    dump_execution_state();
-    printk("*** Dumping CPU%d guest state: ***\n", smp_processor_id());
+    struct cpu_user_regs *regs = _regs;
+    unsigned int cpu = smp_processor_id();
+
+    if ( !guest_mode(regs) )
+    {
+        printk("\n*** Dumping CPU%u host state: ***\n", cpu);
+        show_execution_state(regs);
+    }
     if ( is_idle_vcpu(current) )
-        printk("No guest context (CPU is idle).\n");
+        printk("No guest context (CPU%u is idle).\n", cpu);
     else
+    {
+        printk("*** Dumping CPU%u guest state (d%d:v%d): ***\n",
+               smp_processor_id(), current->domain->domain_id,
+               current->vcpu_id);
         show_execution_state(guest_cpu_user_regs());
+    }
+
+    cpu = cycle_cpu(cpu, dump_execstate_mask);
+    if ( cpu < NR_CPUS )
+    {
+        cpu_clear(cpu, dump_execstate_mask);
+        on_selected_cpus(cpumask_of(cpu), __dump_execstate, NULL, 0);
+    }
+    else
+    {
+        printk("\n");
+
+        console_end_sync();
+        watchdog_enable();
+    }
 }
 
 static void dump_registers(unsigned char key, struct cpu_user_regs *regs)
 {
-    unsigned int cpu;
-
     /* We want to get everything out that we possibly can. */
     watchdog_disable();
     console_start_sync();
@@ -92,21 +117,9 @@ static void dump_registers(unsigned char
     printk("'%c' pressed -> dumping registers\n", key);
 
     /* Get local execution state out immediately, in case we get stuck. */
-    printk("\n*** Dumping CPU%d host state: ***\n", smp_processor_id());
-    __dump_execstate(NULL);
-
-    for_each_online_cpu ( cpu )
-    {
-        if ( cpu == smp_processor_id() )
-            continue;
-        printk("\n*** Dumping CPU%d host state: ***\n", cpu);
-        on_selected_cpus(cpumask_of(cpu), __dump_execstate, NULL, 1);
-    }
-
-    printk("\n");
-
-    console_end_sync();
-    watchdog_enable();
+    cpus_andnot(dump_execstate_mask, cpu_online_map,
+                cpumask_of_cpu(smp_processor_id()));
+    __dump_execstate(regs);
 }
 
 static struct keyhandler dump_registers_keyhandler = {
--- 2010-05-04.orig/xen/include/asm-ia64/linux-xen/asm/ptrace.h 2010-04-19 
09:12:58.000000000 +0200
+++ 2010-05-04/xen/include/asm-ia64/linux-xen/asm/ptrace.h      2010-05-04 
13:22:27.000000000 +0200
@@ -280,7 +280,7 @@ struct switch_stack {
 # define ia64_task_regs(t)             (((struct pt_regs *) ((char *) (t) + 
IA64_STK_OFFSET)) - 1)
 # define ia64_psr(regs)                        ((struct ia64_psr *) 
&(regs)->cr_ipsr)
 #ifdef XEN
-# define guest_mode(regs)              (ia64_psr(regs)->cpl != 0)
+# define guest_mode(regs)              (ia64_psr(regs)->cpl && 
!ia64_psr(regs)->vm)
 # define guest_kernel_mode(regs)       (ia64_psr(regs)->cpl == 
CONFIG_CPL0_EMUL)
 # define vmx_guest_kernel_mode(regs)   (ia64_psr(regs)->cpl == 0)
 # define regs_increment_iip(regs)                                      \

Attachment: dump-exec-state.patch
Description: Text document

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