[XenPPC] IPI problems

[Hollis Blanchard <hollisb@xxxxxxxxxx>]

I mentioned that I accidentally pushed an upstream merge to
xenppc-unstable while it's still broken. There are a couple broken
things. First, DomU console stops mid-string early in boot. Could be an
event channel problem with the ring buffer; haven't investigated.

We seem to have an IPI problem, which causes vcpu_pause() to hang the
system. The following patch, tested on JS20 and JS21, illustrates it.
Before dom0 starts, IPIs work fine. After Linux's mpic_init(), IPIs (as
triggered by the 'I' keyhandler) lock the machine. Actually, it looks
like a message is trying to get out, because after a while we see a '('
emitted (presumably the first character in "(XEN)").

(When I comment out mpic_init() in dom0, Xen IPIs continue to work but
real IRQs (e.g. the IDE controller) fail in dom0.)

Why is this problem occurring only after an upstream merge? I don't
know. It's possible that some common IRQ code has changed to no longer
call the same arch-specific code, but I'm just speculating.



diff -r d6481755ade6 xen/arch/powerpc/setup.c
--- a/xen/arch/powerpc/setup.c  Thu Jan 11 13:39:27 2007 -0600
+++ b/xen/arch/powerpc/setup.c  Fri Jan 12 17:12:27 2007 -0600
@@ -438,7 +438,9 @@ static void __init __start_xen(multiboot
 
     domain_unpause_by_systemcontroller(dom0);
 #ifdef DEBUG_IPI
-    ipi_torture_test();
+    //ipi_torture_test();
+    extern void do_ipi_test(char c);
+    do_ipi_test(0);
 #endif
     startup_cpu_idle_loop();
 }
diff -r d6481755ade6 xen/common/keyhandler.c
--- a/xen/common/keyhandler.c   Thu Jan 11 13:39:27 2007 -0600
+++ b/xen/common/keyhandler.c   Fri Jan 12 17:44:46 2007 -0600
@@ -260,6 +260,16 @@ static void do_debug_key(unsigned char k
                              bit. */
 }
 
+static void got_ipi(void *info)
+{
+    printk("CPU %u got IPI\n", smp_processor_id());
+}
+
+void do_ipi_test(unsigned char key)
+{
+    smp_call_function(got_ipi, NULL, 0, 0);
+}
+
 void initialize_keytable(void)
 {
     open_softirq(KEYPRESS_SOFTIRQ, keypress_softirq);
@@ -286,6 +296,8 @@ void initialize_keytable(void)
 #endif
 
     register_irq_keyhandler('%', do_debug_key,   "Trap to xendbg");
+
+    register_keyhandler('I', do_ipi_test, "IPI test");
 }
 
 /*
diff -r d6481755ade6 xen/drivers/char/console.c
--- a/xen/drivers/char/console.c        Thu Jan 11 13:39:27 2007 -0600
+++ b/xen/drivers/char/console.c        Fri Jan 12 17:09:01 2007 -0600
@@ -246,7 +246,7 @@ static void sercon_puts(const char *s)
 
 /* CTRL-<switch_char> switches input direction between Xen and DOM0. */
 #define SWITCH_CODE (opt_conswitch[0]-'a'+1)
-static int xen_rx = 1; /* FALSE => serial input passed to domain 0. */
+static int xen_rx = 0; /* FALSE => serial input passed to domain 0. */
 
 static void switch_serial_input(void)
 {
diff -r d6481755ade6 xen/include/asm-powerpc/smp.h
--- a/xen/include/asm-powerpc/smp.h     Thu Jan 11 13:39:27 2007 -0600
+++ b/xen/include/asm-powerpc/smp.h     Fri Jan 12 17:03:59 2007 -0600
@@ -52,7 +52,7 @@ void smp_event_check_interrupt(void);
 void smp_event_check_interrupt(void);
 void send_IPI_mask(cpumask_t mask, int vector);
 
-#undef DEBUG_IPI
+#define DEBUG_IPI
 #ifdef DEBUG_IPI
 void ipi_torture_test(void);
 #endif



-- 
Hollis Blanchard
IBM Linux Technology Center


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