Commit:     8a336b0a4b6dfacc8cc5fd617ba1e1904077de2d
Parent:     f82af20e1a028e16b9bb11da081fa1148d40fa6a
Author:     Tim Hockin <[EMAIL PROTECTED]>
AuthorDate: Wed May 2 19:27:19 2007 +0200
Committer:  Andi Kleen <[EMAIL PROTECTED]>
CommitDate: Wed May 2 19:27:19 2007 +0200

    [PATCH] x86-64: Dynamically adjust machine check interval
     We've found that MCEs (specifically DRAM SBEs) tend to come in bunches,
     especially when we are trying really hard to stress the system out.  The
     current MCE poller uses a static interval which does not care whether it
     has or has not found MCEs recently.
     This patch makes the MCE poller adjust the polling interval dynamically.
     If we find an MCE, poll 2x faster (down to 10 ms).  When we stop finding
     MCEs, poll 2x slower (up to check_interval seconds).  The check_interval
     tunable becomes the max polling interval.  The "Machine check events
     logged" printk() is rate limited to the check_interval, which should be
     identical behavior to the old functionality.
     If you start to take a lot of correctable errors (not exceptions), you
     log them faster and more accurately (less chance of overflowing the MCA
     registers).  If you don't take a lot of errors, you will see no change.
     I considered simply reducing the polling interval to 10 ms immediately
     and keeping it there as long as we continue to find errors.  This felt a
     bit heavy handed, but does perform significantly better for the default
     check_interval of 5 minutes (we're using a few seconds when testing for
     DRAM errors).  I could be convinced to go with this, if anyone felt it
     was not too aggressive.
     I used an error-injecting DIMM to create lots of correctable DRAM errors
     and verified that the polling interval accelerates.  The printk() only
     happens once per check_interval seconds.
     This patch is against 2.6.21-rc7.
    Signed-Off-By: Tim Hockin <[EMAIL PROTECTED]>
    Signed-off-by: Andi Kleen <[EMAIL PROTECTED]>
 Documentation/x86_64/machinecheck |    7 ++++++-
 arch/x86_64/kernel/mce.c          |   32 ++++++++++++++++++++++++--------
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/Documentation/x86_64/machinecheck 
index 068a6d9..feaeaf6 100644
--- a/Documentation/x86_64/machinecheck
+++ b/Documentation/x86_64/machinecheck
@@ -36,7 +36,12 @@ between all CPUs.
        How often to poll for corrected machine check errors, in seconds
-       (Note output is hexademical). Default 5 minutes.
+       (Note output is hexademical). Default 5 minutes.  When the poller
+       finds MCEs it triggers an exponential speedup (poll more often) on
+       the polling interval.  When the poller stops finding MCEs, it
+       triggers an exponential backoff (poll less often) on the polling
+       interval. The check_interval variable is both the initial and
+       maximum polling interval.
        Tolerance level. When a machine check exception occurs for a non
diff --git a/arch/x86_64/kernel/mce.c b/arch/x86_64/kernel/mce.c
index 8011a8e..fa26726 100644
--- a/arch/x86_64/kernel/mce.c
+++ b/arch/x86_64/kernel/mce.c
@@ -323,10 +323,13 @@ void mce_log_therm_throt_event(unsigned int cpu, __u64 
 #endif /* CONFIG_X86_MCE_INTEL */
- * Periodic polling timer for "silent" machine check errors.
+ * Periodic polling timer for "silent" machine check errors.  If the
+ * poller finds an MCE, poll 2x faster.  When the poller finds no more
+ * errors, poll 2x slower (up to check_interval seconds).
 static int check_interval = 5 * 60; /* 5 minutes */
+static int next_interval; /* in jiffies */
 static void mcheck_timer(struct work_struct *work);
 static DECLARE_DELAYED_WORK(mcheck_work, mcheck_timer);
@@ -339,7 +342,6 @@ static void mcheck_check_cpu(void *info)
 static void mcheck_timer(struct work_struct *work)
        on_each_cpu(mcheck_check_cpu, NULL, 1, 1);
-       schedule_delayed_work(&mcheck_work, check_interval * HZ);
         * It's ok to read stale data here for notify_user and
@@ -349,17 +351,30 @@ static void mcheck_timer(struct work_struct *work)
         * writes.
        if (notify_user && console_logged) {
+               static unsigned long last_print;
+               unsigned long now = jiffies;
+               /* if we logged an MCE, reduce the polling interval */
+               next_interval = max(next_interval/2, HZ/100);
                notify_user = 0;
                clear_bit(0, &console_logged);
-               printk(KERN_INFO "Machine check events logged\n");
+               if (time_after_eq(now, last_print + (check_interval*HZ))) {
+                       last_print = now;
+                       printk(KERN_INFO "Machine check events logged\n");
+               }
+       } else {
+               next_interval = min(next_interval*2, check_interval*HZ);
+       schedule_delayed_work(&mcheck_work, next_interval);
 static __init int periodic_mcheck_init(void)
-       if (check_interval)
-               schedule_delayed_work(&mcheck_work, check_interval*HZ);
+       next_interval = check_interval * HZ;
+       if (next_interval)
+               schedule_delayed_work(&mcheck_work, next_interval);
        return 0;
@@ -597,12 +612,13 @@ static int mce_resume(struct sys_device *dev)
 /* Reinit MCEs after user configuration changes */
 static void mce_restart(void) 
-       if (check_interval)
+       if (next_interval)
        /* Timer race is harmless here */
        on_each_cpu(mce_init, NULL, 1, 1);       
-       if (check_interval)
-               schedule_delayed_work(&mcheck_work, check_interval*HZ);
+       next_interval = check_interval * HZ;
+       if (next_interval)
+               schedule_delayed_work(&mcheck_work, next_interval);
 static struct sysdev_class mce_sysclass = {
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