linux-kernel - Re: [PATCH v3] x86/hpet: Reduce HPET counter read contention

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Date:	Tue, 12 Apr 2016 04:22:09 +0800
From:	kbuild test robot <lkp@...el.com>
To:	Waiman Long <Waiman.Long@....com>
Cc:	kbuild-all@...org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Jonathan Corbet <corbet@....net>,
	linux-kernel@...r.kernel.org, linux-doc@...nel.org, x86@...nel.org,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Borislav Petkov <bp@...e.de>,
	Andy Lutomirski <luto@...nel.org>,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>,
	Randy Wright <rwright@....com>,
	Waiman Long <Waiman.Long@....com>
Subject: Re: [PATCH v3] x86/hpet: Reduce HPET counter read contention

Hi Waiman,

[auto build test WARNING on tip/auto-latest]
[also build test WARNING on v4.6-rc3 next-20160411]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]

url:    https://github.com/0day-ci/linux/commits/Waiman-Long/x86-hpet-Reduce-HPET-counter-read-contention/20160412-041402
config: x86_64-randconfig-x011-201615 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

>> arch/x86/kernel/hpet.c:786:3: warning: 'hpet_save' defined but not used [-Wunused-variable]
    } hpet_save;
      ^

vim +/hpet_save +786 arch/x86/kernel/hpet.c

   770	 * If multiple CPUs are trying to access the HPET counter at the same time,
   771	 * we don't actually need to read the counter multiple times. Instead, the
   772	 * other CPUs can use the counter value read by the first CPU in the group.
   773	 *
   774	 * A sequence number whose lsb is a lock bit is used to control which CPU
   775	 * has the right to read the HPET counter directly and which CPUs are going
   776	 * to get the indirect value read by the lock holder. For the later group,
   777	 * if the sequence number differs from the expected locked value, they
   778	 * can assume that the saved HPET value is up-to-date and return it.
   779	 */
   780	static struct {
   781		/* Sequence number + bit lock */
   782		int seq ____cacheline_aligned_in_smp;
   783	
   784		/* Current HPET value		*/
   785		u32 hpet ____cacheline_aligned_in_smp;
 > 786	} hpet_save;
   787	#define HPET_SEQ_LOCKED(seq)	((seq) & 1)	/* Odd == locked */
   788	
   789	/*
   790	 * Clock source related code
   791	 */
   792	#ifdef CONFIG_SMP
   793	static cycle_t read_hpet(struct clocksource *cs)
   794	{

---
0-DAY kernel test infrastructure                Open Source Technology Center
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Download attachment ".config.gz" of type "application/octet-stream" (32483 bytes)