linux-kernel - Re: [PATCH] eventfd: support delayed wakeup for non-semaphore eventfd to reduce cpu utilization

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Message-ID: <202304172058.piI49JCE-lkp@intel.com>
Date:   Mon, 17 Apr 2023 20:44:41 +0800
From:   kernel test robot <lkp@...el.com>
To:     wenyang.linux@...mail.com,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>,
        Christian Brauner <brauner@...nel.org>
Cc:     oe-kbuild-all@...ts.linux.dev,
        Wen Yang <wenyang.linux@...mail.com>,
        Christoph Hellwig <hch@....de>, Dylan Yudaken <dylany@...com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Paolo Bonzini <pbonzini@...hat.com>, Fu Wei <wefu@...hat.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] eventfd: support delayed wakeup for non-semaphore
 eventfd to reduce cpu utilization

Hi,

kernel test robot noticed the following build warnings:

[auto build test WARNING on vfs-idmapping/for-next]
[also build test WARNING on linus/master v6.3-rc7]
[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#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/wenyang-linux-foxmail-com/eventfd-support-delayed-wakeup-for-non-semaphore-eventfd-to-reduce-cpu-utilization/20230416-193353
base:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/idmapping.git for-next
patch link:    https://lore.kernel.org/r/tencent_AF886EF226FD9F39D28FE4D9A94A95FA2605%40qq.com
patch subject: [PATCH] eventfd: support delayed wakeup for non-semaphore eventfd to reduce cpu utilization
reproduce:
        # https://github.com/intel-lab-lkp/linux/commit/ea9214e265bae223a795f144d6ddcac65e8e2084
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review wenyang-linux-foxmail-com/eventfd-support-delayed-wakeup-for-non-semaphore-eventfd-to-reduce-cpu-utilization/20230416-193353
        git checkout ea9214e265bae223a795f144d6ddcac65e8e2084
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        make htmldocs

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@...el.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202304172058.piI49JCE-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> Documentation/admin-guide/sysctl/fs.rst:74: WARNING: Title underline too short.

vim +74 Documentation/admin-guide/sysctl/fs.rst

    72	
    73	eventfd_wakeup_delay_msec
  > 74	------------------
    75	Frequent writing of an eventfd can also lead to frequent wakeup of the peer
    76	read process, resulting in significant cpu overhead.
    77	How ever for the NON SEMAPHORE eventfd, if it's counter has a nonzero value,
    78	then a read(2) returns 8 bytes containing that value, and the counter's value
    79	is reset to zero.
    80	So it coule be optimized as follows: N event_writes vs ONE event_read.
    81	By adding a configurable delay after eventfd_write, these unnecessary wakeup
    82	operations are avoided.
    83	The max value is 100 ms.
    84	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests