On 09/01/2011 10:41 AM, Caleb James DeLisle wrote: > I ran some testing by injecting printline statements after the beginning of > each synchronization block > in all of the xwiki codebase and then ran some tests. > > xwiki webstandards test: > pages loaded: 925 > synchronization blocks entered: 2,512,524 > synchronizations per page: 2,716 > > Excluding the first page load on start-up, these are the total > synchronizations from running the > webstandards tests. Note that they don't add up to exactly 2,512,524 because > some were spoiled when > 2 threads tried to write to stdout simultaneously. > > Total Percent Location > 1651401 65.73% XWikiCacheStore.java:115 > 316411 12.59% EmbeddableComponentManager.java:352 > 142094 5.66% XWikiContext.java:260 > 103028 4.10% XWiki.java:5380 > 58151 2.31% XWikiContext.java:282 > 54891 2.18% XWiki.java:5455 > 46324 1.84% DefaultVelocityFactory.java:72 > 46320 1.84% DefaultVelocityFactory.java:82 > 29447 1.17% EmbeddableComponentManager.java:138 > 15010 0.60% DefaultBeanManager.java:204 > 14595 0.58% DefaultXWikiRenderingEngine.java:239 > 10933 0.44% URIClassLoader.java:438 > 3812 0.15% XWiki.java:5406 > 3262 0.13% DefaultVelocityEngine.java:227 > 3262 0.13% DefaultVelocityEngine.java:245 > 2867 0.11% XWikiNotificationManager.java:130 > 1941 0.08% XWikiGroupServiceImpl.java:798 > 958 0.04% XWikiConfigurationService.java:50 > 958 0.04% XWikiNotificationManager.java:254 > 958 0.04% XWikiNotificationManager.java:265 > 957 0.04% XWikiCacheStore.java:704 > 951 0.04% XWikiNotificationManager.java:230 > 949 0.04% XWikiNotificationManager.java:241 > 917 0.04% XWikiNotificationManager.java:219 > 852 0.03% XWikiStatsServiceImpl.java:182 > 371 0.01% XWikiDocumentQueue.java:88 > 351 0.01% XWikiDocumentQueue.java:55 > 142 0.01% XWikiDocumentQueue.java:69 > 112 0.00% XWikiDocumentQueue.java:98 > 66 0.00% AdminAction.java:57 > 24 0.00% RightsManager.java:164 > 15 0.00% EditAction.java:59 > > > UI tests were also run to give a more well rounded view of what real traffic > might look like: > > 1666727 57.98% XWikiCacheStore.java:115 > 463369 16.12% EmbeddableComponentManager.java:352 > 234027 8.14% XWiki.java:5380 > 175972 6.12% XWikiContext.java:260 > 70156 2.44% XWikiContext.java:282 > 65952 2.29% XWiki.java:5455 > 43553 1.52% DefaultVelocityFactory.java:72 > 43552 1.52% DefaultVelocityFactory.java:82 > 33512 1.17% EmbeddableComponentManager.java:138 > 13451 0.47% DefaultBeanManager.java:204 > 9650 0.34% DefaultXWikiRenderingEngine.java:239 > 9450 0.33% XWikiNotificationManager.java:130 > 5176 0.18% XWikiGroupServiceImpl.java:798 > 5019 0.17% URIClassLoader.java:438 > 3965 0.14% XWiki.java:5406 > 2850 0.10% DefaultVelocityEngine.java:227 > 2850 0.10% DefaultVelocityEngine.java:245 > 2717 0.09% XWikiConfigurationService.java:50 > 2694 0.09% XWikiCacheStore.java:704 > 2624 0.09% XWikiNotificationManager.java:219 > 2624 0.09% XWikiNotificationManager.java:230 > 2624 0.09% XWikiNotificationManager.java:241 > 2590 0.09% XWikiNotificationManager.java:254 > 2590 0.09% XWikiNotificationManager.java:265 > 749 0.03% XWikiDocumentQueue.java:69 > 718 0.02% XWikiStatsServiceImpl.java:182 > 554 0.02% XWikiDocumentQueue.java:88 > 550 0.02% EmbeddableComponentManager.java:201 > 476 0.02% XWikiDocumentQueue.java:55 > 406 0.01% XWikiHibernateVersioningStore.java:142 > 403 0.01% XWikiNotificationManager.java:140 > 403 0.01% XWikiNotificationManager.java:155 > 403 0.01% XWikiNotificationManager.java:167 > 403 0.01% XWikiNotificationManager.java:181 > 403 0.01% XWikiNotificationManager.java:194 > 403 0.01% XWikiNotificationManager.java:206 > 282 0.01% XWikiDocumentQueue.java:98 > 209 0.01% EditAction.java:59 > 101 0.00% RightsManager.java:164 > 81 0.00% AdminAction.java:57 > 61 0.00% EmbeddableComponentManager.java:289 > 52 0.00% EmbeddableComponentManager.java:256 > 44 0.00% LucenePlugin.java:656 > 35 0.00% InlineAction.java:39 > 23 0.00% DefaultCSRFToken.java:130 > 19 0.00% MutableHttpServletRequestFactory.java:43 > 15 0.00% AbstractGenericComponentManager.java:93 > 13 0.00% LucenePlugin.java:450 > 5 0.00% XWikiNotificationManager.java:56 > 2 0.00% MacroRepository.java:65 > 2 0.00% XWiki.java:408 > 1 0.00% ActivityStreamCleaner.java:89 > 1 0.00% EmbeddableComponentManager.java:163 > 1 0.00% EmbeddableComponentManager.java:269 > 1 0.00% RightsManagerListener.java:85 > 1 0.00% SchedulerPlugin.java:561 > 1 0.00% StackingComponentEventManager.java:69 > 1 0.00% XWikiGroupServiceImpl.java:150 > 1 0.00% XWikiGroupServiceImpl.java:162 > 1 0.00% XWikiGroupServiceImpl.java:180 > 1 0.00% XWikiHibernateBaseStore.java:142 > 1 0.00% XWikiHibernateBaseStore.java:265 > 1 0.00% XWikiHibernateBaseStore.java:557 > 1 0.00% XWiki.java:5493 > 1 0.00% XWiki.java:5515 > > > > These numbers seem to be quite conclusive that XWikiCacheStore.java:115 is > the lowest hanging fruit > in the synchronization field. An examination of XWikiCacheStore reveals that > the "per load" > synchronization should be avoidable if it is not lazy initialized and is > flushed differently.
Lazy initialization is bad. Historically, it has been done this way in many places since the context is not available too early. This XWikiContext class is a very bad item causing a lot of problems in the old core. > Is synchronization the best place to attack for performance gains? > Synchronization cost is difficult to measure because it varies based on > number of processor cores and > processor sockets. In the worst case, the caches in multiple cores on > multiple processor sockets all > need to be flushed and this would be the case with high contention mutexes. > As a matter of good practice, I think we should reduce the amount of > synchronization as much as is reasonable. Yes, it is a valid goal to reduce as much as possible the list of synchronized methods and blocks, and attempts in this direction have been previously made. IMO bad synchronization is a very good candidate for performance improvements, since that many synchronizations for one request makes it very likely that most of the time only one request gets to be executed, making XWiki behave worse than a single-threaded application. -- Sergiu Dumitriu http://purl.org/net/sergiu/ _______________________________________________ devs mailing list [email protected] http://lists.xwiki.org/mailman/listinfo/devs
