[Xen-changelog] Using a slow serial console with sync_console on SMP leaves an

[Xen patchbot -unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID 5ff5117291add571df9d7f3973b0a69a0515c04f
# Parent  5e617fd4850427ac4ac235969b36d78935103f19
Using a slow serial console with sync_console on SMP leaves an
unusable system: it gets into a flood of

Timer ISR/0: Time went backwards: delta=-3566279 cpu_delta=16433721
shadow=2019998373 off=420435384 processed=2444000000
cpu_processed=2424000000
 0: 2424000000
 1: 2444000000

messages which swamps the console and leaves things almost, but not
quite, completely hung.  It is a simple matter to ratelimit these
printks, which completely eliminates the problem.

diff -r 5e617fd48504 -r 5ff5117291ad 
linux-2.6-xen-sparse/arch/xen/i386/kernel/time.c
--- a/linux-2.6-xen-sparse/arch/xen/i386/kernel/time.c  Sat Dec  3 00:51:36 2005
+++ b/linux-2.6-xen-sparse/arch/xen/i386/kernel/time.c  Sat Dec  3 09:44:01 2005
@@ -560,7 +560,8 @@
        }
        while (!time_values_up_to_date(cpu));
 
-       if (unlikely(delta < -1000000LL) || unlikely(delta_cpu < 0)) {
+       if ((unlikely(delta < -1000000LL) || unlikely(delta_cpu < 0))
+           && printk_ratelimit()) {
                printk("Timer ISR/%d: Time went backwards: "
                       "delta=%lld cpu_delta=%lld shadow=%lld "
                       "off=%lld processed=%lld cpu_processed=%lld\n",

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