Re: [PATCH 3.6-rc6] cpufreq/powernow-k8: workqueue user shouldn't migrate the kworker to another CPU

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Tuesday, September 18, 2012, Tejun Heo wrote:
> So, with work_on_cpu() reimplementation just posted[1], we can do the
> following instead.  Functionally it's about the same but less ugly.
> Ugly as it may be, I think the previous open coded version is better
> suited as a fix and for -stable.  Thoughts?

I'd prefer this one to go into v3.7 along with the work_on_cpu() patch
and then the open-coded version to go to -stable after the mainline one
has got some testing coverage.

Thanks,
Rafael


> [1] https://lkml.org/lkml/2012/9/18/430
> 
>  drivers/cpufreq/powernow-k8.c |   63 ++++++++++++++++++++++--------------------
>  1 file changed, 34 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/cpufreq/powernow-k8.c b/drivers/cpufreq/powernow-k8.c
> index c0e8164..1a40935 100644
> --- a/drivers/cpufreq/powernow-k8.c
> +++ b/drivers/cpufreq/powernow-k8.c
> @@ -35,7 +35,6 @@
>  #include <linux/slab.h>
>  #include <linux/string.h>
>  #include <linux/cpumask.h>
> -#include <linux/sched.h>	/* for current / set_cpus_allowed() */
>  #include <linux/io.h>
>  #include <linux/delay.h>
>  
> @@ -1139,16 +1138,23 @@ static int transition_frequency_pstate(struct powernow_k8_data *data,
>  	return res;
>  }
>  
> -/* Driver entry point to switch to the target frequency */
> -static int powernowk8_target(struct cpufreq_policy *pol,
> -		unsigned targfreq, unsigned relation)
> +struct powernowk8_target_arg {
> +	struct cpufreq_policy		*pol;
> +	unsigned			targfreq;
> +	unsigned			relation;
> +};
> +
> +static long powernowk8_target_fn(void *arg)
>  {
> -	cpumask_var_t oldmask;
> +	struct powernowk8_target_arg *pta = arg;
> +	struct cpufreq_policy *pol = pta->pol;
> +	unsigned targfreq = pta->targfreq;
> +	unsigned relation = pta->relation;
>  	struct powernow_k8_data *data = per_cpu(powernow_data, pol->cpu);
>  	u32 checkfid;
>  	u32 checkvid;
>  	unsigned int newstate;
> -	int ret = -EIO;
> +	int ret;
>  
>  	if (!data)
>  		return -EINVAL;
> @@ -1156,29 +1162,16 @@ static int powernowk8_target(struct cpufreq_policy *pol,
>  	checkfid = data->currfid;
>  	checkvid = data->currvid;
>  
> -	/* only run on specific CPU from here on. */
> -	/* This is poor form: use a workqueue or smp_call_function_single */
> -	if (!alloc_cpumask_var(&oldmask, GFP_KERNEL))
> -		return -ENOMEM;
> -
> -	cpumask_copy(oldmask, tsk_cpus_allowed(current));
> -	set_cpus_allowed_ptr(current, cpumask_of(pol->cpu));
> -
> -	if (smp_processor_id() != pol->cpu) {
> -		printk(KERN_ERR PFX "limiting to cpu %u failed\n", pol->cpu);
> -		goto err_out;
> -	}
> -
>  	if (pending_bit_stuck()) {
>  		printk(KERN_ERR PFX "failing targ, change pending bit set\n");
> -		goto err_out;
> +		return -EIO;
>  	}
>  
>  	pr_debug("targ: cpu %d, %d kHz, min %d, max %d, relation %d\n",
>  		pol->cpu, targfreq, pol->min, pol->max, relation);
>  
>  	if (query_current_values_with_pending_wait(data))
> -		goto err_out;
> +		return -EIO;
>  
>  	if (cpu_family != CPU_HW_PSTATE) {
>  		pr_debug("targ: curr fid 0x%x, vid 0x%x\n",
> @@ -1196,7 +1189,7 @@ static int powernowk8_target(struct cpufreq_policy *pol,
>  
>  	if (cpufreq_frequency_table_target(pol, data->powernow_table,
>  				targfreq, relation, &newstate))
> -		goto err_out;
> +		return -EIO;
>  
>  	mutex_lock(&fidvid_mutex);
>  
> @@ -1209,9 +1202,8 @@ static int powernowk8_target(struct cpufreq_policy *pol,
>  		ret = transition_frequency_fidvid(data, newstate);
>  	if (ret) {
>  		printk(KERN_ERR PFX "transition frequency failed\n");
> -		ret = 1;
>  		mutex_unlock(&fidvid_mutex);
> -		goto err_out;
> +		return 1;
>  	}
>  	mutex_unlock(&fidvid_mutex);
>  
> @@ -1220,12 +1212,25 @@ static int powernowk8_target(struct cpufreq_policy *pol,
>  				data->powernow_table[newstate].index);
>  	else
>  		pol->cur = find_khz_freq_from_fid(data->currfid);
> -	ret = 0;
>  
> -err_out:
> -	set_cpus_allowed_ptr(current, oldmask);
> -	free_cpumask_var(oldmask);
> -	return ret;
> +	return 0;
> +}
> +
> +/* Driver entry point to switch to the target frequency */
> +static int powernowk8_target(struct cpufreq_policy *pol,
> +		unsigned targfreq, unsigned relation)
> +{
> +	struct powernowk8_target_arg pta = { .pol = pol, .targfreq = targfreq,
> +					     .relation = relation };
> +
> +	/*
> +	 * Must run on @pol->cpu.  cpufreq core is responsible for ensuring
> +	 * that we're bound to the current CPU and pol->cpu stays online.
> +	 */
> +	if (smp_processor_id() == pol->cpu)
> +		return powernowk8_target_fn(&pta);
> +	else
> +		return work_on_cpu(pol->cpu, powernowk8_target_fn, &pta);
>  }
>  
>  /* Driver entry point to verify the policy and range of frequencies */
> 
>