[ovirt-devel] [ATTN] GWT Debug mode is now 2x faster!
Vojtech Szocs
vszocs at redhat.com
Fri Aug 8 14:41:58 UTC 2014
----- Original Message -----
> From: "Greg Sheremeta" <gshereme at redhat.com>
> To: devel at ovirt.org
> Cc: awels at redhat.com, ecohen at redhat.com, "Vojtech Szocs" <vszocs at redhat.com>
> Sent: Wednesday, August 6, 2014 2:09:03 PM
> Subject: [ATTN] GWT Debug mode is now 2x faster!
>
> [changing the subject to be more noticeable]
>
> All,
>
> Alexander did some great work making GWT debug mode at least 2x faster.
> It is now *very* usable.
Indeed, well done Alex!
>
> I have previously avoided it, but now it's pretty awesome. If you have
> avoided
> it like me, give it a try!
>
> Tip:
> make gwt-debug DEBUG_MODULE=webadmin
> DEV_EXTRA_BUILD_FLAGS_GWT_DEFAULTS="-Dgwt.cssResourceStyle=pretty"
> will un-obfuscate CSS classes for you. Very helpful with debugging UI stuff.
>
> Greg
>
> ----- Original Message -----
> > From: "Vojtech Szocs" <vszocs at redhat.com>
> > To: devel at ovirt.org
> > Cc: awels at redhat.com, ecohen at redhat.com, gshereme at redhat.com
> > Sent: Wednesday, July 30, 2014 11:19:46 AM
> > Subject: Re: GWT debug slowness.
> >
> > Hi Alex,
> >
> > (adding devel list to share it with others)
> >
> > I really appreciate that you took the time to analyze GWT EventBus
> > activity!
> >
> > As we discussed on IRC, @ProxyEvent in AbstractSubTabPresenter is the most
> > likely cause of overall UI slowness after successful user authentication.
> > Fix for this should be rather easy and harmless, please add me as reviewer
> > once you come up with the relevant patch.
> >
> > Another thing is "refresh on logout" for all (both) GWT applications. This
> > is mainly due to planned SSO changes (there will be a dedicated interactive
> > login page for entire Engine); for us it means that "login" section of all
> > GWT applications will be unnecessary. Before that, however, we can already
> > implement "refresh on logout". As a nice side effect, we can remove some of
> > our infra (UiCommonInitEvent & friends) to make it more simple.
> >
> > Please find some more comments below (inline).
> >
> > Thanks,
> > Vojtech
> >
> >
> > ----- Original Message -----
> > > From: "Alexander Wels" <awels at redhat.com>
> > > To: vszocs at redhat.com
> > > Cc: ecohen at redhat.com, gshereme at redhat.com
> > > Sent: Friday, July 25, 2014 7:59:56 PM
> > > Subject: Re: GWT debug slowness.
> > >
> > > On Friday, July 25, 2014 09:28:33 AM Alexander Wels wrote:
> > > > Vojtech,
> > > >
> > > > I know you suggested that maybe the event bus was getting overloaded
> > > > with
> > > > events might be the cause of the slowness in the GWT debug mode. So I
> > > > modified the event bus implementation to record the number of events,
> > > > their
> > > > handlers, and the occurrences of those events.
> > > >
> > > > This is right after the login page is loaded.
> > > > +---------------------------------------------------+-----------+-----------
> > > > +
> > > > |Type |handlers |fired
> > > > ||
> > > > +---------------------------------------------------+-----------+-----------
> > > > +
> > > > |event: ApplicationFocusChangeEvent: |0 |2
> > > > || event: LockInteractionEvent: |2 |2
> > > > | | event: NavigationEvent: |0 |1
> > > > | | event: PlaceRequestInternalEvent: |111
> > > > | | |1
> > > > | | event: ResetPresentersEvent: |1
> > > > | | |1
> > > > | | event: RevealRootLayoutContentEvent: |1
> > > > ||1 |
> > > > +---------------------------------------------------+-----------+-----------
> > > > +
> >
> > Just for clarification:
> >
> > * ApplicationFocusChangeEvent - fired by our infra whenever browser/window
> > gains or looses focus (we use this to throttle UiCommon model refresh
> > timers, i.e. when out of focus, lower the refresh rate)
> >
> > * LockInteractionEvent - fired by GWTP infra, indicates that UI interaction
> > should be avoided because the application is currently in transition from
> > one place to another (in practice, invisible "glass" <div> element covers
> > the entire viewport during transition, see RootPresenter.RootView)
> >
> > Note: we had plans to provide some "In progress..." label (just like you
> > see in Gmail) to make this obvious to end users, there's also RFE on this
> >
> > * NavigationEvent - fired by GWTP infra, it's a hook we don't use
> >
> > * PlaceRequestInternalEvent - fired by GWTP infra, PlaceManagerImpl fires
> > this event to ask all proxies: "which one of you can reveal a presenter
> > with name token xxx" (i.e. "dataCenters-clusters")
> >
> > Note: handler count is high because EACH presenter proxy adds handler
> > for this event.
> >
> > * ResetPresentersEvent - fired by GWTP infra, after transition to new place
> > is complete, trigger "onReset" lifecycle method on all presenters present
> > on "reveal path" (from leaf to root)
> >
> > * RevealRootLayoutContentEvent - fired by GWTP infra, this makes GWTP root
> > presenter/view reveal within the browser/window viewport
> >
> > > >
> > > > This is right after you login, and the VM main tab is displayed
> > > > +---------------------------------------------------+-----------+-----------
> > > > +
> > > > |Type |handlers |fired
> > > > ||
> > > > +---------------------------------------------------+-----------+-----------
> > > > +
> > > > |event: UiCommonInitEvent: |715 |1
> > > > || event: RestApiSessionAcquiredEvent: |1 |1
> > > > | | event: UserLoginChangeEvent: |3 |1
> > > > | | event: ApplicationFocusChangeEvent: |80
> > > > | | |2
> > > > | | event: LockInteractionEvent: |2
> > > > | | |3
> > > > | | event: NavigationEvent: |0
> > > > ||1 | event: PlaceRequestInternalEvent: |205
> > > > | |2 | event: InitializeEvent:
> > > > | ||167
> > > > | |170 | event: SSOTokenChangeEvent:
> > > > | ||1
> > > > | |1 | event: ResetPresentersEvent:
> > > > | ||1
> > > > | |1 | event: RevealRootLayoutContentEvent:
> > > > ||1 |1 |
> > > > +---------------------------------------------------+-----------+-----------
> > > > +
> >
> > Most of these events are fired by our own infra.
> >
> > UiCommonInitEvent has so many handlers due to following components:
> >
> > * TabModelProvider (access to UiCommon models)
> > * AbstractActionPanel (for each "action button" definition!)
> > * UiCommandButtonDefinition (button bound to UiCommon model "command")
> > * AbstractRefreshManager (controlling refresh of list models)
> > * ModelBoundTab (tab's properties bound to UiCommon model properties)
> > * AbstractActionTable (added recently, for search string change stuff)
> > * some more classes (UserPortalConfigurator, WebAdminConfigurator,
> > SearchPanelPresenterWidget)
> >
> > Each component mentioned above needs to be notified when relevant
> > UiCommon model changes. As you might know, on each login, current
> > CommonModel (root model) instance is thrown away (if any) and new
> > CommonModel instance is created. CommonModel in turn creates its
> > "child" models, which create their "child" models, etc. This is,
> > in my opinion, one of the BIGGEST flaws of UiCommon code design;
> > it makes models tightly coupled with all subsequent consequences.
> >
> > (As with any kind of design, once it's put to use on a bigger scale,
> > it's really hard to change in a way that's consistent, safe and not
> > too invasive.)
> >
> > I was, for a very long time, convinced that we can still have a nice
> > single-page AJAX GWT UI application that doesn't need "refresh on
> > logout", i.e. application that properly handles UiCommon. In light
> > of upcoming SSO changes, however, we should do "refresh on logout".
> >
> > This will allow us to:
> >
> > * (future) eliminate GWT login screen entirely, in favor of SSO
> > interactive login page
> >
> > * (now) eliminate complex infra (UiCommonInitEvent & friends)
> > in order to properly use UiCommon in single-page application
> > scenario
> >
> > (BTW, PlaceRequestInternalEvent handler count increased from 111
> > to 205, not sure what is the exact cause of this, I'd have to dig
> > deeper into GWTP infra code.)
> >
> > > >
> > > > As you can see the number of events fired is not all that high, the
> > > > only
> > > > somewhat strange thing, is that there are a huge number of
> > > > UiCommonInitEvent handlers. Doing a quick search reveals that every tab
> > > > provider, every refresh manager (refresh button) and a whole bunch of
> > > > other
> > > > widgets all have handlers, which does explain the huge number of
> > > > handlers.
> >
> > Yup. All of this is needed to properly use UiCommon in single-page
> > scenario, i.e. UI components need to be notified whenever UiCommon
> > model instances change (typically due to UI login).
> >
> > If UiCommon wasn't designed to instantiate whole model tree right
> > on successful login (replacing old instances with new ones), we
> > wouldn't have to deal with this issue. The whole UiCommonInitEvent
> > infra is to ensure we use UiCommon in a way it was designed to be
> > used.
> >
> > > >
> > > > In short I don't think the slowness is related to the EventBus at this
> > > > point
> > > > in time and I will have to look else where for the problem.
> > > >
> > >
> > > To respond to myself (isn't talking to yourself a sign of insanity?).
> >
> > Nah :) re-thinking what you thought previously is a good thing.
> >
> > > I did
> > > some profiling
> > > while running in GWT debug mode, and I discovered the following sequence
> > > of
> > > events
> > > which seems to be related to the huge number of UiCommonInitEvent
> > > handlers.
> > >
> > > I found that most of the time was taken during the UiCommonInitEvent
> > > firing.
> > > which
> > > led me to see which one of the handlers was taking so long. So I profiled
> > > the
> > > time each
> > > handler took to complete. I noticed something really strange, the tab
> > > providers all
> > > took between 0 and 1ms.
> >
> > It's because TabModelProvider#onCommonModelChange is not special in any
> > way.
> >
> > > But every single sub tab presenter for every single
> > > sub tab
> > > was taking between 500 and 3000ms depending on the presenter.
> >
> > It's because creation of presenter triggeres creation of view, and creation
> > of view triggers HTML DOM operations which can be expensive, depending on
> > the complexity of the view/HTML.
> >
> > It's very important to realize that presenter must be first created and
> > bound
> > (presenter's proxy takes care of this) and only THEN presenter is able to
> > deal
> > with events such as UiCommonInitEvent.
> >
> > @ProxyEvent causes event handler to be registered on proxy itself -
> > whenever
> > such event occurs, proxy will create & bind presenter and call
> > corresponding
> > @ProxyEvent method on presenter.
> >
> > This is also why you're observing 500 .. 3000ms times.
> >
> > > Since we have
> > > like
> > > 200 of those presenters, every single one of them was being
> > > called/initialized and
> > > taking time, even if we never used them. It turns out we had a ProxyEvent
> > > on
> > > AbstractSubTabPresenter, which would cause every single sub tab presenter
> > > to
> > > load
> > > (since they were code splitted, this takes a lot of requests).
> > >
> > > @ProxyEvent
> > > public void onUiCommonInit(UiCommonInitEvent event) {
> > > ...initialize some handlers...
> > > }
> >
> > Correct! @ProxyEvent is a "lazy" programmer's trick to ensure that
> > presenter
> > never misses on any event of given type.
> >
> > The downside is that when such event (UiCommonInitEvent) happens, possibly
> > TONS of presenters (and associated views) will be created & bound.
> >
> > As we discussed, we can improve this by moving relevant code into onBind()
> > presenter lifecycle callback.
> >
> > >
> > > So what I did to solve the problem, I removed the @ProxyEvent, and
> > > renamed
> > > it
> > > initializeHandlers. Then instead of them being called in response to the
> > > onUiCommonInit event, I put the call in onBind of the presenter. If I
> > > understand the
> > > GWTP life cycle correctly this should have the same effect as before (the
> > > handlers are
> > > initialized before they are needed) and thus everything should work the
> > > same.
> >
> > onBind() is called once per lifetime of bound object.
> >
> > All presenters are singletons, so onBind() is called once in their
> > lifetime.
> >
> > A common trick is to do following in onBind():
> >
> > // For any future occurences of event
> > registerHandler(eventBus.addHandler(..foo()..));
> >
> > // For the first time, if needed
> > foo();
> >
> > (Assuming foo() contains init logic sensitive to given event.)
> >
> > >
> > > The results that I have observed so far from these changes:
> > > - GWT debug mode login takes ~50s instead of 4:30.
> > > - The number of requests to the engine dropped from around 80 to around
> > > 20.
> > > - In compiled mode the login is much much faster.
> > > - I haven't checked the memory usage, but I am guessing it will be much
> > > lower
> > > with all
> > > presenters not being in memory until they are needed.
> >
> > Great stuff! Maybe we could squeeze this in 3.5 too :)
> >
> > >
> > > My only concern at this point, is that I am not aware of a particular
> > > sequence that
> > > requires the presenters to be present somewhere, and now they are not,
> > > and
> > > something doesn't work.
> >
> > Communication is mostly done through events, so EventBus is essentially
> > the only direct dependency between all presenters. In practice, there
> > might be exceptions, but in general, events are to decouple presenters.
> >
> > As for your concern - I don't think we should worry about it. GWTP infra
> > will always load presenters when they are needed (i.e. for the reveal of
> > requested place). Our code CAN load them even earlier, if needed (like
> > with @ProxyEvent).
> >
> > > In my limited testing everything worked the same as
> > > before,
> > > but obviously I haven't touched every single tab and sub tab.
> > >
> > > One more thing to note, the proxy event has been like that since before I
> > > joined Red
> > > Hat, so again this is NOT the cause for the recent slowdown, but
> > > something
> > > in
> > > the
> > > presenters could have added some time to each of them causing the huge
> > > number
> > > of
> > > them combined to have a large impact.
> >
> > The number of sub tabs (and associated UiCommon models) grew over time,
> > so there's (I think) cumulative performance impact of @ProxyEvent in
> > AbstractSubTabPresenter.
> >
> > Sure, there might be other bottlenecks, but we can improve this right
> > now and gain substantial speed/performance improvement.
> >
> > (Great job!)
> >
> > >
> > > Alexander
> > >
> > > > Alexander
> > >
> > >
> >
>
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