[PATCH v3 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path

[Yicong Yang]

On 2022/6/9 18:14, kernel test robot wrote:
> Hi Yicong,
> 
> Thank you for the patch! Perhaps something to improve:
> 
> [auto build test WARNING on tip/sched/core]
> [also build test WARNING on linus/master v5.19-rc1 next-20220609]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Yicong-Yang/sched-fair-Wake-task-within-the-cluster-when-possible/20220608-181847
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 991d8d8142cad94f9c5c05db25e67fa83d6f772a
> config: x86_64-randconfig-a006 (https://download.01.org/0day-ci/archive/20220609/202206091846.fm1bYjWk-lkp@intel.com/config)
> compiler: gcc-11 (Debian 11.3.0-3) 11.3.0
> reproduce (this is a W=1 build):
>         # https://github.com/intel-lab-lkp/linux/commit/f2b15e8641f351783c1d47bc654ace164300b7f1
>         git remote add linux-review https://github.com/intel-lab-lkp/linux
>         git fetch --no-tags linux-review Yicong-Yang/sched-fair-Wake-task-within-the-cluster-when-possible/20220608-181847
>         git checkout f2b15e8641f351783c1d47bc654ace164300b7f1
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash kernel/sched/
> 
> If you fix the issue, kindly add following tag where applicable
> Reported-by: kernel test robot <lkp at intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
>    kernel/sched/fair.c: In function 'select_idle_cpu':
>>> kernel/sched/fair.c:6381:36: warning: passing argument 2 of 'scan_cluster' makes integer from pointer without a cast [-Wint-conversion]

I didn't change the scan_cluster() stub correspondingly, which leads to this error. thanks for catching this and will fix in v4.

>     6381 |         idle_cpu = scan_cluster(p, cpus, target, &nr);
>          |                                    ^~~~
>          |                                    |
>          |                                    struct cpumask *
>    kernel/sched/fair.c:6327:59: note: expected 'int' but argument is of type 'struct cpumask *'
>     6327 | static inline int scan_cluster(struct task_struct *p, int prev_cpu, int target, int *nr)
>          |                                                       ~~~~^~~~~~~~
>    kernel/sched/fair.c: At top level:
>    kernel/sched/fair.c:11114:6: warning: no previous prototype for 'task_vruntime_update' [-Wmissing-prototypes]
>    11114 | void task_vruntime_update(struct rq *rq, struct task_struct *p, bool in_fi)
>          |      ^~~~~~~~~~~~~~~~~~~~
> 
> 
> vim +/scan_cluster +6381 kernel/sched/fair.c
> 
>   6332	
>   6333	/*
>   6334	 * Scan the LLC domain for idle CPUs; this is dynamically regulated by
>   6335	 * comparing the average scan cost (tracked in sd->avg_scan_cost) against the
>   6336	 * average idle time for this rq (as found in rq->avg_idle).
>   6337	 */
>   6338	static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool has_idle_core, int target)
>   6339	{
>   6340		struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
>   6341		int i, cpu, idle_cpu = -1, nr = INT_MAX;
>   6342		struct rq *this_rq = this_rq();
>   6343		int this = smp_processor_id();
>   6344		struct sched_domain *this_sd;
>   6345		u64 time = 0;
>   6346	
>   6347		this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
>   6348		if (!this_sd)
>   6349			return -1;
>   6350	
>   6351		cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
>   6352	
>   6353		if (sched_feat(SIS_PROP) && !has_idle_core) {
>   6354			u64 avg_cost, avg_idle, span_avg;
>   6355			unsigned long now = jiffies;
>   6356	
>   6357			/*
>   6358			 * If we're busy, the assumption that the last idle period
>   6359			 * predicts the future is flawed; age away the remaining
>   6360			 * predicted idle time.
>   6361			 */
>   6362			if (unlikely(this_rq->wake_stamp < now)) {
>   6363				while (this_rq->wake_stamp < now && this_rq->wake_avg_idle) {
>   6364					this_rq->wake_stamp++;
>   6365					this_rq->wake_avg_idle >>= 1;
>   6366				}
>   6367			}
>   6368	
>   6369			avg_idle = this_rq->wake_avg_idle;
>   6370			avg_cost = this_sd->avg_scan_cost + 1;
>   6371	
>   6372			span_avg = sd->span_weight * avg_idle;
>   6373			if (span_avg > 4*avg_cost)
>   6374				nr = div_u64(span_avg, avg_cost);
>   6375			else
>   6376				nr = 4;
>   6377	
>   6378			time = cpu_clock(this);
>   6379		}
>   6380	
>> 6381		idle_cpu = scan_cluster(p, cpus, target, &nr);
>   6382		if ((unsigned int)idle_cpu < nr_cpumask_bits)
>   6383			return idle_cpu;
>   6384	
>   6385		for_each_cpu_wrap(cpu, cpus, target + 1) {
>   6386			if (has_idle_core) {
>   6387				i = select_idle_core(p, cpu, cpus, &idle_cpu);
>   6388				if ((unsigned int)i < nr_cpumask_bits)
>   6389					return i;
>   6390	
>   6391			} else {
>   6392				if (--nr <= 0)
>   6393					return -1;
>   6394				idle_cpu = __select_idle_cpu(cpu, p);
>   6395				if ((unsigned int)idle_cpu < nr_cpumask_bits)
>   6396					break;
>   6397			}
>   6398		}
>   6399	
>   6400		if (has_idle_core)
>   6401			set_idle_cores(target, false);
>   6402	
>   6403		if (sched_feat(SIS_PROP) && !has_idle_core) {
>   6404			time = cpu_clock(this) - time;
>   6405	
>   6406			/*
>   6407			 * Account for the scan cost of wakeups against the average
>   6408			 * idle time.
>   6409			 */
>   6410			this_rq->wake_avg_idle -= min(this_rq->wake_avg_idle, time);
>   6411	
>   6412			update_avg(&this_sd->avg_scan_cost, time);
>   6413		}
>   6414	
>   6415		return idle_cpu;
>   6416	}
>   6417	
>