[PATCH] limit CPU time spent in kipmid (version 4)

[Martin Wilck]

Hi all,

I am sorry for the long silence. I am sending here a new version of my 
patch which takes into account Bela's suggestions (well, most of them).
I compiled and tested it with 2.6.29.4, the results are similar as 
before. By setting kipmid_max_busy_us to a value between 100 and 500, it 
is possible to bring down kipmid CPU load to practically 0 without 
loosing too much ipmi throughput performance.

Please give me some feedback whether this patch will get merged, and if 
not, what improvement is needed.

Regards
Martin

--
Dr. Martin Wilck
PRIMERGY System Software Engineer
x86 Server Engineering

Fujitsu Technology Solutions GmbH
Heinz-Nixdorf-Ring 1
33106 Paderborn, Germany

Phone:			++49 5251 525 2796
Fax:			++49 5251 525 2820
Email:			martin.wilck@xxxxxxxxxxxxxx
Internet:		http://ts.fujitsu.com
Company Details:	http://de.ts.fujitsu.com/imprint.html
Signed-off-by: martin.wilck@xxxxxxxxxxxxxx
--- linux-2.6.29.4/drivers/char/ipmi/ipmi_si_intf.c	2009-05-19 01:52:34.000000000 +0200
+++ linux-2.6.29-rc8/drivers/char/ipmi/ipmi_si_intf.c	2009-06-04 15:30:34.855398091 +0200
@@ -297,6 +297,9 @@
 static int force_kipmid[SI_MAX_PARMS];
 static int num_force_kipmid;
 
+static unsigned int kipmid_max_busy_us[SI_MAX_PARMS];
+static int num_max_busy_us;
+
 static int unload_when_empty = 1;
 
 static int try_smi_init(struct smi_info *smi);
@@ -927,23 +930,56 @@
 	}
 }
 
+#define ipmi_si_set_not_busy(timespec) \
+	do { (timespec)->tv_nsec = -1; } while (0)
+#define ipmi_si_is_busy(timespec) ((timespec)->tv_nsec != -1)
+
+static int ipmi_thread_busy_wait(enum si_sm_result smi_result,
+				 const struct smi_info *smi_info,
+				 struct timespec *busy_until)
+{
+	unsigned int max_busy_us = 0;
+
+	if (smi_info->intf_num < num_max_busy_us)
+		max_busy_us = kipmid_max_busy_us[smi_info->intf_num];
+	if (max_busy_us == 0 || smi_result != SI_SM_CALL_WITH_DELAY)
+		ipmi_si_set_not_busy(busy_until);
+	else if (!ipmi_si_is_busy(busy_until)) {
+		getnstimeofday(busy_until);
+		timespec_add_ns(busy_until, max_busy_us*NSEC_PER_USEC);
+	} else {
+		struct timespec now;
+		getnstimeofday(&now);
+		if (unlikely(timespec_compare(&now, busy_until) > 0)) {
+			ipmi_si_set_not_busy(busy_until);
+			return 0;
+		}
+	}
+	return 1;
+}
+
 static int ipmi_thread(void *data)
 {
 	struct smi_info *smi_info = data;
 	unsigned long flags;
 	enum si_sm_result smi_result;
+	struct timespec busy_until;
 
+	ipmi_si_set_not_busy(&busy_until);
 	set_user_nice(current, 19);
 	while (!kthread_should_stop()) {
+		int busy_wait;
 		spin_lock_irqsave(&(smi_info->si_lock), flags);
 		smi_result = smi_event_handler(smi_info, 0);
 		spin_unlock_irqrestore(&(smi_info->si_lock), flags);
+		busy_wait = ipmi_thread_busy_wait(smi_result, smi_info,
+						  &busy_until);
 		if (smi_result == SI_SM_CALL_WITHOUT_DELAY)
 			; /* do nothing */
-		else if (smi_result == SI_SM_CALL_WITH_DELAY)
+		else if (smi_result == SI_SM_CALL_WITH_DELAY && busy_wait)
 			schedule();
 		else
-			schedule_timeout_interruptible(1);
+			schedule_timeout_interruptible(0);
 	}
 	return 0;
 }
@@ -1213,6 +1249,11 @@
 MODULE_PARM_DESC(unload_when_empty, "Unload the module if no interfaces are"
 		 " specified or found, default is 1.  Setting to 0"
 		 " is useful for hot add of devices using hotmod.");
+module_param_array(kipmid_max_busy_us, uint, &num_max_busy_us, 0644);
+MODULE_PARM_DESC(kipmid_max_busy_us,
+		 "Max time (in microseconds) to busy-wait for IPMI data before"
+		 " sleeping. 0 (default) means to wait forever. Set to 100-500"
+		 " if kipmid is using up a lot of CPU time.");
 
 
 static void std_irq_cleanup(struct smi_info *info)