Wei Yang <richardw.y...@linux.intel.com> writes: > On Thu, Feb 21, 2019 at 12:46:18PM +0800, Huang, Ying wrote: >>Wei Yang <richardw.y...@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 <l...@intel.com> >>>>Date: Wed Feb 20 14:21:19 2019 +0800 >>>> >>>> backfile klist_node in struct device for debugging >>>> >>>> Signed-off-by: 0day robot <l...@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?
Yes. I guess these size change may affect system performance. Some other objects may share slab page with these objects. Best Regards, Huang, Ying >>Best Regards, >>Huang, Ying >> >>>> >>>>Best Regards, >>>>Rong Chen