Messages in this thread | | | Date | Thu, 21 Feb 2019 14:02:18 +0800 | From | Wei Yang <> | Subject | Re: [LKP] [driver core] 570d020012: will-it-scale.per_thread_ops -12.2% regression |
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On Thu, Feb 21, 2019 at 12:46:18PM +0800, Huang, Ying wrote: >Wei Yang <richardw.yang@linux.intel.com> writes: > >> On Thu, Feb 21, 2019 at 11:10:49AM +0800, kernel test robot wrote: >>>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 >>> >> >> Do you have the comparison between a36dc70b810afe9183de2ea18f and the one >> before 570d020012? >> >>> >>>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 */ >> >> Hmm... because this is not properly aligned? >> >> struct klist_node { >> void *n_klist; /* never access directly */ >> struct list_head n_node; >> struct kref n_ref; >> }; >> >> Except struct kref has one "int" type, others are pointers. >> >> But... I am still confused. > >I guess because the size of struct device is changed, it influences some >alignment changes in the system. Thus influence the benchmark score. >
That's interesting.
I wrote a module to see the exact size of these two structure on my x86_64.
sizeof(struct device) = 736 = 8 * 92 sizeof(struct device_private) = 160 = 8 * 20 sizeof(struct klist_node) = 32 = 8 * 4
Even klist_node has one 4 byte field, c complier would pack the structure to make it aligned. Which system alignment it would affect?
After the patch, size would change like this:
struct device 736 -> 704 struce device_private 160 -> 192
Would this size change affect system?
>Best Regards, >Huang, Ying > >>> >>>Best Regards, >>>Rong Chen
-- Wei Yang Help you, Help me
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