Commit ae74e823 authored by Martin Wilck's avatar Martin Wilck Committed by Linus Torvalds
Browse files

ipmi: add parameter to limit CPU usage in kipmid 



In some cases kipmid can use a lot of CPU.  This adds a way to tune the
CPU used by kipmid to help in those cases.  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.  Not setting the value, or setting the value to zero,
operation is unaffected.

Signed-off-by: default avatarMartin Wilck <martin.wilck@ts.fujitsu.com>
Signed-off-by: default avatarCorey Minyard <cminyard@mvista.com>
Cc: Jean Delvare <jdelvare@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f1eb1332

Documentation/IPMI.txt

+12 −0
Original line number Diff line number Diff line
@@ -365,6 +365,7 @@ You can change this at module load time (for a module) with: 
       regshifts=<shift1>,<shift2>,...

       slave_addrs=<addr1>,<addr2>,...

       force_kipmid=<enable1>,<enable2>,...

       kipmid_max_busy_us=<ustime1>,<ustime2>,...

       unload_when_empty=[0|1]



Each of these except si_trydefaults is a list, the first item for the
@@ -433,6 +434,7 @@ kernel command line as: 
       ipmi_si.regshifts=<shift1>,<shift2>,...

       ipmi_si.slave_addrs=<addr1>,<addr2>,...

       ipmi_si.force_kipmid=<enable1>,<enable2>,...

       ipmi_si.kipmid_max_busy_us=<ustime1>,<ustime2>,...



It works the same as the module parameters of the same names.
@@ -450,6 +452,16 @@ force this thread on or off. If you force it off and don't have 
interrupts, the driver will run VERY slowly.  Don't blame me,

these interfaces suck.



Unfortunately, this thread can use a lot of CPU depending on the

interface's performance.  This can waste a lot of CPU and cause

various issues with detecting idle CPU and using extra power.  To

avoid this, the kipmid_max_busy_us sets the maximum amount of time, in

microseconds, that kipmid will spin before sleeping for a tick.  This

value sets a balance between performance and CPU waste and needs to be

tuned to your needs.  Maybe, someday, auto-tuning will be added, but

that's not a simple thing and even the auto-tuning would need to be

tuned to the user's desired performance.



The driver supports a hot add and remove of interfaces.  This way,

interfaces can be added or removed after the kernel is up and running.

This is done using /sys/modules/ipmi_si/parameters/hotmod, which is a

drivers/char/ipmi/ipmi_si_intf.c

+64 −2
Original line number Diff line number Diff line
@@ -295,6 +295,9 @@ struct smi_info { 
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);
@@ -925,23 +928,77 @@ static void set_run_to_completion(void *send_info, int i_run_to_completion) 
	}

}



/*

 * Use -1 in the nsec value of the busy waiting timespec to tell that

 * we are spinning in kipmid looking for something and not delaying

 * between checks

 */

static inline void ipmi_si_set_not_busy(struct timespec *ts)

{

	ts->tv_nsec = -1;

}

static inline int ipmi_si_is_busy(struct timespec *ts)

{

	return ts->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;

}





/*

 * A busy-waiting loop for speeding up IPMI operation.

 *

 * Lousy hardware makes this hard.  This is only enabled for systems

 * that are not BT and do not have interrupts.  It starts spinning

 * when an operation is complete or until max_busy tells it to stop

 * (if that is enabled).  See the paragraph on kimid_max_busy_us in

 * Documentation/IPMI.txt for details.

 */

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;

}
@@ -1212,6 +1269,11 @@ module_param(unload_when_empty, int, 0); 
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)

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