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Date: Tue, 18 Sep 2012 22:30:15 +0200
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Tejun Heo <tj@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
linux-kernel@...r.kernel.org, cpufreq@...r.kernel.org,
linux-pm@...r.kernel.org, Duncan <1i5t5.duncan@....net>,
Andreas Herrmann <andreas.herrmann3@....com>
Subject: Re: [PATCH 3.6-rc6] cpufreq/powernow-k8: workqueue user shouldn't migrate the kworker to another CPU
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 */
>
>
--
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