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    SubjectRe: [LKP] [driver core] 570d020012: will-it-scale.per_thread_ops -12.2% regression
    On Tue, Feb 19, 2019 at 01:19:04PM +0100, Greg Kroah-Hartman wrote:
    > On Tue, Feb 19, 2019 at 08:59:45AM +0800, Wei Yang wrote:
    > > On Mon, Feb 18, 2019 at 03:54:42PM +0800, kernel test robot wrote:
    > > >Greeting,
    > > >
    > > >FYI, we noticed a -12.2% regression of will-it-scale.per_thread_ops due to commit:
    > > >
    > > >
    > > >commit: 570d0200123fb4f809aa2f6226e93a458d664d70 ("driver core: move device->knode_class to device_private")
    > > >https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
    > > >
    > >
    > > This is interesting.
    > >
    > > I didn't expect the move of this field will impact the performance.
    > >
    > > The reason is struct device is a hotter memory than device->device_private?
    > >
    > > >in testcase: will-it-scale
    > > >on test machine: 288 threads Knights Mill with 80G memory
    > > >with following parameters:
    > > >
    > > > nr_task: 100%
    > > > mode: thread
    > > > test: unlink2
    > > > cpufreq_governor: performance
    > > >
    > > >test-description: Will It Scale takes a testcase and runs it from 1 through to n parallel copies to see if the testcase will scale. It builds both a process and threads based test in order to see any differences between the two.
    > > >test-url: https://github.com/antonblanchard/will-it-scale
    > > >
    > > >In addition to that, the commit also has significant impact on the following tests:
    > > >
    > > >+------------------+---------------------------------------------------------------+
    > > >| testcase: change | will-it-scale: will-it-scale.per_thread_ops -29.9% regression |
    > > >| test machine | 288 threads Knights Mill with 80G memory |
    > > >| test parameters | cpufreq_governor=performance |
    > > >| | mode=thread |
    > > >| | nr_task=100% |
    > > >| | test=signal1 |
    >
    > Ok, I'm going to blame your testing system, or something here, and not
    > the above patch.
    >
    > All this test does is call raise(3). That does not touch the driver
    > core at all.
    >
    > > >+------------------+---------------------------------------------------------------+
    > > >| testcase: change | will-it-scale: will-it-scale.per_thread_ops -16.5% regression |
    > > >| test machine | 288 threads Knights Mill with 80G memory |
    > > >| test parameters | cpufreq_governor=performance |
    > > >| | mode=thread |
    > > >| | nr_task=100% |
    > > >| | test=open1 |
    > > >+------------------+---------------------------------------------------------------+
    >
    > Same here, open1 just calls open/close a lot. No driver core
    > interaction at all there either.
    >
    > So are you _sure_ this is the offending patch?

    Hi Greg,

    We did an experiment, recovered the layout of struct device. and we
    found the regression is gone. I guess the regession is not from the
    patch but related to the struct layout.


    tests: 1
    testcase/path_params/tbox_group/run: will-it-scale/performance-thread-100%-unlink2/lkp-knm01

    570d0200123fb4f8 a36dc70b810afe9183de2ea18f
    ---------------- --------------------------
    %stddev change %stddev
    \ | \
    237096 14% 270789 will-it-scale.workload
    823 14% 939 will-it-scale.per_thread_ops


    tests: 1
    testcase/path_params/tbox_group/run: will-it-scale/performance-thread-100%-signal1/lkp-knm01

    570d0200123fb4f8 a36dc70b810afe9183de2ea18f
    ---------------- --------------------------
    %stddev change %stddev
    \ | \
    93.51 ± 3% 48% 138.53 ± 3% will-it-scale.time.user_time
    186 40% 261 will-it-scale.per_thread_ops
    53909 40% 75507 will-it-scale.workload


    tests: 1
    testcase/path_params/tbox_group/run: will-it-scale/performance-thread-100%-open1/lkp-knm01

    570d0200123fb4f8 a36dc70b810afe9183de2ea18f
    ---------------- --------------------------
    %stddev change %stddev
    \ | \
    447722 22% 546258 ± 10% will-it-scale.time.involuntary_context_switches
    226995 19% 269751 will-it-scale.workload
    787 19% 936 will-it-scale.per_thread_ops



    commit a36dc70b810afe9183de2ea18faa4c0939c139ac
    Author: 0day robot <lkp@intel.com>
    Date: Wed Feb 20 14:21:19 2019 +0800

    backfile klist_node in struct device for debugging

    Signed-off-by: 0day robot <lkp@intel.com>

    diff --git a/include/linux/device.h b/include/linux/device.h
    index d0e452fd0bff2..31666cb72b3ba 100644
    --- a/include/linux/device.h
    +++ b/include/linux/device.h
    @@ -1035,6 +1035,7 @@ struct device {
    spinlock_t devres_lock;
    struct list_head devres_head;

    + struct klist_node knode_class_test_by_rongc;
    struct class *class;
    const struct attribute_group **groups; /* optional groups */

    Best Regards,
    Rong Chen
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