linux-kernel - Re: [PATCH] sched/cputime: Mitigate performance regression in times()/clock

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Date:	Tue, 26 Jul 2016 22:43:20 +0800
From:	kbuild test robot <lkp@...el.com>
To:	Giovanni Gherdovich <ggherdovich@...e.cz>
Cc:	kbuild-all@...org, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <mgalbraith@...e.de>,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.com>,
	Giovanni Gherdovich <ggherdovich@...e.cz>
Subject: Re: [PATCH] sched/cputime: Mitigate performance regression in
 times()/clock_gettime()

Hi,

[auto build test ERROR on tip/sched/core]
[also build test ERROR on v4.7 next-20160726]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Giovanni-Gherdovich/sched-cputime-Mitigate-performance-regression-in-times-clock_gettime/20160726-221216
config: mips-allyesconfig (attached as .config)
compiler: mips-linux-gnu-gcc (Debian 5.4.0-6) 5.4.0 20160609
reproduce:
        wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=mips 

All errors (new ones prefixed by >>):

   kernel/sched/core.c: In function 'task_sched_runtime':
>> kernel/sched/core.c:3009:3: error: implicit declaration of function 'prefetch' [-Werror=implicit-function-declaration]
      prefetch((&p->se)->cfs_rq->curr);
      ^
   cc1: some warnings being treated as errors
   make[2]: *** [kernel/sched/core.o] Error 1
   make[2]: Target '__build' not remade because of errors.
   make[1]: *** [kernel/sched/] Error 2

vim +/prefetch +3009 kernel/sched/core.c

  3003		 * Must be ->curr _and_ ->on_rq.  If dequeued, we would
  3004		 * project cycles that may never be accounted to this
  3005		 * thread, breaking clock_gettime().
  3006		 */
  3007		if (task_current(rq, p) && task_on_rq_queued(p)) {
  3008	#if defined(CONFIG_FAIR_GROUP_SCHED)
> 3009			prefetch((&p->se)->cfs_rq->curr);
  3010			prefetch(&(&p->se)->cfs_rq->curr->exec_start);
  3011	#endif
  3012			update_rq_clock(rq);

---
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