Re: [PATCH 1/4] IPMI: Add parameter to limit CPU usage in kipmid

[Corey Minyard <minyard@acm.org>]

Jean Delvare wrote:
> Hi Corey, Linus,
>
> On Wednesday 03 March 2010 05:14:38 pm Corey Minyard wrote:
>   
>> From: Martin Wilck <martin.wilck@ts.fujitsu.com>
>>
>> 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: Martin Wilck <martin.wilck@ts.fujitsu.com>
>> Cc: Jean Delvare <jdelvare@suse.de>
>> Signed-off-by: Corey Minyard <cminyard@mvista.com>
>> ---
>> This patch has been discussed quite a bit, and I believe all issues with it
>> have been resolved.  It's not great, but nobody has a better way to handle
>> the problem.
>>     
>
> I still can't see this patch in Linus' tree as of 2.6.34-rc1. It has been 
> waiting for sooo long already, can we finally get it in? Linus, will you apply 
> it? Or should it go through Andrew?
>   
It's already in Andrew's patches.  It would be good if this could go in 
for 2.6.34, I think it has been through enough review and such.

-corey

> Thanks.
>
>   
>> Index: linux-2.6.32/drivers/char/ipmi/ipmi_si_intf.c
>> ===================================================================
>> --- linux-2.6.32.orig/drivers/char/ipmi/ipmi_si_intf.c
>> +++ linux-2.6.32/drivers/char/ipmi/ipmi_si_intf.c
>> @@ -294,6 +294,9 @@ 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);
>> @@ -924,23 +927,77 @@ static void set_run_to_completion(void *
>>  	}
>>  }
>>
>> +/*
>> + * 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;
>>  }
>> @@ -1211,6 +1268,11 @@ 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)
>> Index: linux-2.6.32/Documentation/IPMI.txt
>> ===================================================================
>> --- linux-2.6.32.orig/Documentation/IPMI.txt
>> +++ linux-2.6.32/Documentation/IPMI.txt
>> @@ -365,6 +365,7 @@ You can change this at module load time
>>         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 for
>>  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
>>     
>
>