Re: [Xen-devel] [PATCH, v2] reduce 'd' debug key's global impact

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

Actually I have to withdraw this version too - calling on_selected_cpus()
from a call-function handler just isn't a valid thing to do.

The best alternative I can currently think of is to hook this as an
unlikely code path into an existing IPI handler (e.g. for x86 the
event check one), since sending a simple IPI doesn't have similar
problems.

Jan

>>> "Jan Beulich" <JBeulich@xxxxxxxxxx> 05.05.10 17:34 >>>
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 alternatively block each CPU as it prints
rather than one CPU for a very long time (using the alternative key
handling toggle introduced with an earlier patch). Also 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
actually interesting).

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

--- 2010-05-04.orig/xen/arch/ia64/linux-xen/smp.c       2010-05-05 
16:42:36.000000000 +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  2010-05-05 16:42:36.000000000 +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  2010-05-05 16:49:24.000000000 +0200
@@ -71,14 +71,44 @@ 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());
+    }
+
+    if ( !alt_key_handling )
+        return;
+
+    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)
@@ -91,15 +121,20 @@ static void dump_registers(unsigned char
 
     printk("'%c' pressed -> dumping registers\n", key);
 
+    if ( alt_key_handling )
+        cpus_andnot(dump_execstate_mask, cpu_online_map,
+                    cpumask_of_cpu(smp_processor_id()));
+
     /* 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);
+    __dump_execstate(regs);
+
+    if ( alt_key_handling )
+        return;
 
     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);
     }
 
--- 2010-05-04.orig/xen/include/asm-ia64/linux-xen/asm/ptrace.h 2010-05-05 
16:42:36.000000000 +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)                                      \



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