Category: News

Vulkan and Metal – a Quick Status Update

Just a quick update on our progress with Vulkan and Metal. We last spoke about this on the live feed a few weeks ago, but we’re a little further along. Here’s the summary:

  • Plane-Maker and Airfoil Maker run in Vulkan and Metal.
  • X-Plane runs in Vulkan and Metal up to the main menu (e.g. the app starts) but can’t yet fly or show scenery.
  • The Vulkan and Metal code runs on Mac, Windows and Linux.
  • The Vulkan code runs on Nvidia, AMD and Intel drivers.
  • All shaders are ported.
  • All of the zoo animals (abstractions around part of the graphics engine) are now complete. We killed off the last 2 or 3 since the live feed.

For the last two weeks, Sidney and I have been working to port all rendering passes to the new code, so we don’t have to go through OpenGL to fly the aircraft. I lost a few days dealing with this:

That turned out to be a single if statement that got reversed deep in the mesh drawing code during one of the porting steps, resulting in some of the runway lights being replaced with random pieces of … heck, I never figured out what the wrong mesh was, just that it came from some other unrelated part of the sim and changed as the camera moved. To make matters worse, the error only appeared on the Mac, so we couldn’t use Windows OpenGL debugging tools to find the issue.

The silver lining is that once we are all Vulkan/Metal, we’ll have at least four separate debugging tools to go after bugs like this.

We don’t have measurements of performance yet; once we can sit in an aircraft in X-Plane running Metal or Vulkan, we can at least get some initial performance numbers.

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X-Plane 11.32

We’ve posted X-Plane 11.32 release candidate two – it contains very few changes from release candidate one. If you think RC2 changed your framerate from RC1 (for better or worse), it is imaginary.

The big item for RC2 is that X-Plane now uses our own replicating METAR servers. NOAA weather was plagued by 404s when the server posted METARs didn’t meet the date/time scheme X-Plane expected. Our own server should serve the latest weather we have, whatever that is.

Over the last few weeks we have spent a tremendous amount of developer time investigating reports of instability, crashes and performance problems, and the results have been quite unsatisfying. We really haven’t found a series of smoking guns we could fix to improve stability. We have learned some things about X-Plane’s performance and stability though. The rest of this post gets into the weeds; if you tune out (and I won’t fault you if you do) the TL;DR is: please turn on our anonymous analytics, and click “send” if you get the crash report form. The more gathered data we get about crashes, the better shot we have at addressing the issues.

Crash Rates and Plugins

X-Plane’s overall crash rate (all causes is approximately 14% – which is to say, for all of our users using analytics, for every 100 times they launch X-Plane, the sim quits in a way we did not expect or want 14 times. This number has been remarkably stable – it’s not a ton different between 11.26, 11.30, 11.31 or the 11.32 beta.

The sim quitting on purpose because of bad content is not considered a crash. For example, if you load a DSF with a missing .ter file, the sim will refuse to proceed and quit. This failure mode is user hostile in that you can’t fly, but it’s not a crash – the refusal to load is the code working according to design. While I would like to make this code less hostile to users, it’s also worth noting that these cases are ones where the author of the scenery pack would have been able to fix this if they had loaded their own work even just once. That is, they are caused by an add-on that should not have shipped.

(There is an in-between area where an add-on is mis-installed because it has a library dependency that the user hasn’t met. This is a deployment problem that really needs to be solved, but it’s orthogonal to true app crashes.)

We categorize crashes into plugin and non-plugin crashes; starting with 11.32 we actually get a statistical picture of this.  A crash is a plugin crash (and you see the “we crashed because of a plugin: XSquawkBox” or whatever) if the sim crashed while executing code on behalf of a plugin or inside the plugin on the main thread.

There are a bunch of cases where plugins do not get correctly tagged – in particular, we regularly see crashes on random worker threads spawned by plugins; since we don’t know whose thread it is, we can’t blame the plugin. For example, the FF A320 crashing inside CEF on a worker thread is registered as an X-Plane crash (and we see it in our auto-reporting view) but it’s not our code and there’s nothing we can do about it.

One thing I’d like to do in future patches is improve diagnostics. The rate of actual blamed plugin crashes appears so far to be quite low, and given that we do see uncaught plugin crashes in our data on a regular basis, I think this is a case where add-on authors can only fix what they can see. If we can attribute all plugin crashes to plugins, then the plugin authors can catch their own bugs. Better diagnostics also helps a user remove a troublesome add-on in the case where that would help.

“Known” Crashes

We have a few cases where X-Plane hits an error condition and deals with it by crashing. This is pretty bad, drives up our crash rate, and is something we need to fix to be less user hostile. For example, if a PNG file is bad (either corrupt contents or the sector on disk that backs it has gone bad) then X-Plane’s response is usually to mysteriously crash. Besides being rude, the crash gives an end user no idea which file is bad, and thus no way to fix it. X-Plane ships with something like 9000+ PNG files and over 2500 DDS files, not counting add-ons, so if we don’t tell you which file is bad, you’re not going to find it by poking around.

FMOD sound bank incompatibilities is another example – if you have two aircraft sharing a byte-wise copy of the same FMOD data (e.g. command-D duplicate the C172) loaded at once – then our FMOD loading code fails and then registers as a crash. The code is working exactly as we designed it, but the design isn’t robust enough. As we’ve learned, in the real world users duplicate aircraft (and their FMOD packs) on disk all the time.

The crashes in this category are things where we’re being user-unfriendly and better code would make these problems go away or leave users with a way to actually fix them. But they’re not case of “weird stuff inside the sim blew up.”

Persistent Stability Problems

In the crash data we do also see a few persistent stability problems. There’s some kind of crash in the ATC system that we’ve seen for a very long time but we don’t know how to reproduce. It’s a case where if enough users do enough random stuff, we hit an edge case in the ATC system that isn’t handled correctly. The solution here is to embed more diagnostics at the crash site until we can understand it from the reports we get from users. Please hit “send” when you crash – don’t worry about filling in the fields – it’s the report itself that we need.

We also see a lot of crashes inside the OpenGL drivers, from all of NVidia, AMD and Intel. Because the IHVs don’t share symbols and source code with us, we really can’t tell what went wrong in these cases.

My hope is that with Vulkan we’ll have better options for in-driver crashes. With Vulkan, they redesigned the error checking model: error checking is a feature you enable (via a configuration option at app startup) that brings a layer of code in on top of the driver to check what the app is doing. With error checking off we get the fastest framerate, and with error checking on we get slow framerate (more error checking means more slow) but some really great diagnostics.

(To put this in perspective: when Sidney ran the Vulkan version of Airfoil-Maker on Linux with the wrong driver installed and no error checking, it rebooted his entire Window server!  So no error checking really means: no error checking.)

Since error checking is optional and selectable when the app runs, we could put an option into X-Plane to run in “safe mode” – if a user is hitting persistent stability problems in the driver, that user could turn on validation and possibly capture an error in X-Plane itself that would otherwise just be “the driver crashed.”

Running Out of Memory

I’ve worked with a few users to try to track down the out of memory problems we’ve heard about, and there isn’t an obvious pattern here. Some users report running out of memory in 11.30, but when put back on 11.26, find that they still run out of memory. We get more out-of-GPU-memory complaints on 11.30, but that might be because a few cases in 11.26 that were crashes due to running out of memory now report the problem in an orderly way. In 11.26 they were just mysterious crashes with a “send” form.

In the cases we’ve seen, the user running out of memory was often…actually running out of memory – that is, the surprising thing is not the crash but that X-Plane ever worked at all on those settings. The fundamental problem we face is that we have no visibility into what the OpenGL driver is doing with GPU memory. The OpenGL tries to manage memory no matter how much we ask for, and if it fails, we don’t know what went wrong.

The good news is: we have much better options for Vulkan. With Vulkan, we manage memory, which means we know what’s going on, and we can take steps to avoid out of memory crashes. If we do run out of memory, it should be for much more obvious reasons. We’re still analyzing what we can do about memory with Metal, but the choices should still be better than OpenGL.

The only advice I can offer now if you are seeing persistent memory crashes is: turn your settings down or use less add-ons. If you push X-Plane to the limits of your hardware, it may work for a while and then fail.

Performance

Sidney has looked at a lot of performance data from users who reported low framerate, and in almost every case, the performance has been as-expected. The most common case we see is users with relatively low single-core CPU performance hitting low framerate at high rendering settings while their GPU is bored. To put some numbers on this, if your CPU’s single-core geekbench score is down around 2000, you are almost certainly CPU bound, way at the bottom of what’s okay for X-Plane, and a new GPU won’t help.

As of now, X-Plane cannot use large numbers of cores (e.g. a 32-core machine is useless) and gets only limited performance boosts for framerate with multiple cores under some circumstances. This is something we are working to change in the future, but it’s not going to change quickly. If you are looking to improve performance with hardware, single core speed is still the most important metric.*

In a few rare cases we saw performance that was disproportionately bad compared to what we’d expect from an old CPU. We’re trying to gather more data from these users but the case is rare enough that we haven’t gotten a useful report yet. If we find a smoking gun, we can act on it.

Like memory, Vulkan will help with diagnosing performance. With Vulkan, more of the code is written by us and the Vulkan code we run has very predictable timing. So when we get complaints about performance, we’ll be in a much better position to understand what is slow and why.

What’s Next

I’m actually not sure what the next patch will be, but we do have a bunch of bug fixes to 11.30 waiting to go out once we have stabilization under control. I also have a pile of bugs that I have not yet fixed that are high on my priority list where something in 11.26 stopped working in 11.30. So if you have filed a bug that’s not fixed, we have not forgotten about it – it’s either next to come out or possibly on the short list.

* Yes, we realize that this dependence on single core speed is bad. It’s just going to take time to move to Vulkan and then offload the single thread.

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Going Live in 10… 9… 8…

EDIT: See the recording of the Q&A session here on YouTube!

We’ve been posting about this on social media for a bit, but realized we hadn’t talked about it here.

Today at 11 am Eastern (16:00 UTC; click here for time zone math) we’ll be doing another live Q&A on our YouTube channel. We’ll be taking questions in the YouTube comments, but if you can’t make it live, we’ll try to answer a few questions from the comments on this post.

In case you missed the first, second, and third (part 1 & part 2) rounds of this, this is a streaming broadcast featuring:

  • Austin Meyer, owner & creator of X-Plane
  • Ben Supnik, desktop product manager
  • Chris Serio, mobile product manager
  • Alex Unruh, art director
  • …and a handful of other special X-Plane friends.
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X-Plane 11.32: Real Weather Fix, GPU Memory Fix (Maybe)

X-Plane 11.32 is available as a opt-in public beta for Laminar and Steam users. If you are seeing the sim randomly crash more frequently than before the X-Plane 11.30 series, please try this beta.

NOAA dropped non-HTTPS access to weather data today, causing Real Weather to fail; this is fixed in this beta build. The NOAA issue should not affect any weather add-ons, nor will the fix.

Edit: 11.32 release candidate 1 appears to fix only part of the problem; upper winds are all “zero”. I’m traveling now so it will be a few days before this is fixed.

Most of the crashes we’ve seen have been the GPU driver failing to get us memory. We don’t know if 11.32 will help, but we have tried a change to how we work with the driver that is more like 11.26 and more conservative, that we are hoping will be more stable.

Edit: there have been very few auto-reported crashes with 11.32 – less so than the number of “it crashed” blog comments!  Remember to it “send” on the auto-reporter if X-Plane crashes; you don’t need to enter any data, just hitting send captures your Log file and where the sim crashed, which is what we need most.

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11.31 and Bug Squashing

Inevitably after a large update to X-Plane like 11.30, new bugs go undetected during the beta process. We do a quick update to try to kill off these bugs as quickly as we can, e.g. X-Plane 11.11, 11.26, 11.31.

Yesterday we shipped 11.31. Unfortunately this isn’t the end of X-Plane 11.30 bugs, and in two cases, 11.31 appears to have introduced new problems.

We are working now on X-Plane 11.32, and our rough plan is:

  1. Fix all the really serious bugs (crashes, performance so bad you can’t fly) and ship that ASAP.
  2. Fix the rest of the lingering 11.30 bugs.
  3. Take a moment to question life choices.

If you are seeing crashes in X-Plane 11.30 or 11.31, the most useful thing you can do is to auto-report them, preferably with your email address in the report, so that we can contact you to run special builds.

The rest of this post is an update on the state of some of these bugs.

Driver Bugs

Older Intel OpenGL drivers contained a bug in their pre-processor that caused them to reject our HDR shadowing shaders. I rewrote the shaders to work around this bug for 11.31, and the rewrite has exposed a bug in OS X OpenGL drivers from 10.10.5. I have already fixed this and confirmed the fix with users who still run 10.10.5, so this bug fix will ship in 11.32 for sure. In the meantime, turn off HDR to work around the problem.

Also, if you are a Mac user running 10.10.5, consider updating to a newer Mac OS!

Weather Crash

The most mysterious crash we see is new to 11.31 – a mysterious crash in the weather code. This crash is mysterious to us because nothing changed anywhere near this code from 11.30 to 11.31. The crash reports also don’t make a ton of sense – Sidney and I spent a few hours last night staring at disassembly and being baffled.

I have been contacting users who auto-reported this crash, and fortunately the response to running some test builds for this has been quite positive. I’m hoping to narrow down the change that caused this so that we can wrap our heads around what went wrong.

This weather crash is the one I am most concerned about because it is both unrelated to anything we changed and introduced in 11.31 – a tiny release designed to stabilize, not destabilize the sim. I don’t have a work-around at the time because I don’t have anything like causal steps to reproduce.

Please do not contact me with “I have a crash, can I help” – if we haven’t seen your crash report, there’s no way for you to know if the crash you have is this one or something else. If your email address is in your auto-reports, we can ping you.

Running Out of Mapped GPU Memory

The largest source of instability we’ve seen recently comes from 11.30, and it’s the GPU not being able to provide X-Plane with mapped memory. Since we radically changed the rendering engine in 11.30 (as part of our port toward Vulkan) I am not surprised to see a major GPU problem, but it is still a top priority to fix it. This bug is equally common in 11.30 and 11.31, appears to affect AMD and NVidia windows users (but perhaps AMD more – we’re not sure), but isn’t something we see on our lab machines.  Sidney and I have some ideas on how to at least work around the problem so that people can fly.

Performance Problems

We’ve heard a lot of chatter about performance problems and complaints about performance loss, and we are collecting detailed performance reports from users so we can see what’s going on. Since the performance tests are automated, it’s relatively quick for us to gather this data.

So far, while we have seen a lot of mediocre performance (and mediocre hardware!), we have not yet measured via tests the kind of “catastrophic” performance problems that one might expect from the amount of complaining on forums, etc. That doesn’t mean there isn’t a serious problem out there, it just means we haven’t seen it.

For performance, my view is: if we find something truly awful (e.g. the sim used to run at 25 fps and now runs at 5 fps after the update), we’ll go fix it. I don’t want to make anyone’s copy of X-Plane impossible to use.

But if someone is seeing a 5-10% loss of performance, at this point it’s better to ignore it, because the same engineers who would analyze and fix the performance problems (Sidney and myself) are the ones who are doing the Vulkan port, and the Vulkan port gives us a better shot at fixing performance than trying to beat more performance out of the OpenGL driver stack. In fact, even analyzing the problem is more possible with Vulkan, because the OpenGL drivers do a number of expensive things that they give us no visibility into.

To give you an example of what I mean: we captured performance data from a user with an older Ryzen 16-core CPU and a GeForce 1080 GTX. Our analysis showed: 20-30 fps in the highest fps test (basically everything maxed out), 50-60 fps in medium settings, and 60-70 fps at the lowest settings. At all times, the GeForce 1080 was not maxed out and the CPU was the bottleneck.

Here’s the thing: the older Ryzen CPU has a single-core Geekbench score about as good as my 2014 iMac – that is, it’s not a top tier CPU, it’s old, and it was never optimized for single threaded performance. The user’s system is unbalanced for X-Plane (a lot more GPU than needed for that CPU), and 20-30 fps with everything maxed out is all I would expect from a CPU of that performance level.

So there’s no sign that the machine is underperforming our expectations. And the obvious thing to do to make the system faster is to be more multi-core (since the machine has 16 cores). And that means: focus on Vulkan.

So when it comes to performance, I’m going to beg patience and try to not lose momentum on the Vulkan/Metal port. In the long term it’s a better way to help everyone go faster. If we find something truly bad though, we will go and investigate more.

I don’t know what the ETA is for 11.32, but my plan is days, not weeks. The crash bugs are our top priority right now.

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X-Plane 11.31 Release Candidate 1 – Bug Squashing

X-Plane 11.31 is available to test – run our installer, update X-Plane, and check “get betas”. Full list of bug fixes here.

X-Plane 11.31 contains bug fixes that we could get done quickly, that almost made it into 11.30, and that were high priority, e.g. crashing on some Intel GPUs is fixed, and the external visuals don’t randomly lose sync.

We do still have some other fixes to get in at a later time. For example, there are a number of particle replay bugs where X-Plane isn’t saving the data needed to replay the particle effect; we will patch those in a separate patch where we can add more data to the .rep/.sit structures.

Some users have reported performance bugs, and we are gathering data and looking into them, but I’m not treating them as a five-alarm fire. We’re at a point where we are making rapid progress on the Vulkan port, and I don’t want that progress to grind to a halt as we investigate OpenGL performance problems; we already know that the long term solution to OpenGL performance problems is going to be Vulkan, not stabbing the OpenGL code repeatedly with a fork in the hope that it’s better behaved.

If we find something blatantly wrong with the OpenGL code in 11.30, we’ll fix it, but when it comes to ensuring performance, the very fact that the engine is OpenGL and not Vulkan limits us. At this point the IHVs are making their best performance analysis tools for Vulkan and Metal, not OpenGL, and Vulkan provides an API where the drivers performance is deterministic. (What we’ve seen so far is differing OpenGL performance for basically the same hardware drivers.)

X-Plane 11.30 was a really big code update to X-Plane – it had a major update on our route to re-writing the rendering engine, hence all of the rendering bugs we’re fixing. Over the next few updates I think we’ll have less code change as we stabilize, paired with art updates. We’ll take gateway airports and we have some landmarks ready to go.

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X-Plane 11.30 Is Final

It’s out the door! (Steam should go “final” tomorrow morning, but you can get the final now – it’s still marked as a “beta”.)  Here’s everything that happened.

I expect we’ll do an 11.31 bug fix patch in the next week or two – 11.30 release candidate three was just critical fixes, e.g. fixing crashes on startup for Nvidia users with Windows 10 and the moon and stars aligned just right. Some less super-critical bugs are fixed and waiting for the bug fix patch.

 

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X-Plane 11.30 Release Candidate 1 and Toe Brakes

X-Plane 11.30 Release Candidate 1 is out – we fixed a lot of bugs!

As you can tell by the release name, we’re getting ready to kick this thing out the door.  Most of the team is no longer working on 11.30, and those of us who are are trying to make very small, tactical changes to not further screw things up. I wouldn’t bet against an RC2 (we’ve needed more than one try for all of the “really big” patches we’ve done in the last decade) but at this point if you haven’t tested your add-on against 11.30, you’re really late to the party.

Auto Toe Brakes

Flight simulators sometimes have to deal with unrealistic problems specific to being simulators and not real airplanes. One category of these “unrealistic problems” is dealing with user input hardware that is less complex than the real control inputs of the airplane. You might have a single throttle lever on your joystick, and not the 4 throttles with reversers of the 747. You might not have a twist axis or rudder pedals. You might be flying with a mouse!

Automatic toe brakes are a feature where X-Plane automatically applies differential toe brakes at times that we think might be useful if you don’t have toe brake hardware and no plugin is controlling the toe brakes. For example, an aircraft with a free-castering nose-wheel might be impossible to steer at low speeds without toe brakes. (You can’t turn the nose wheel directly, and the rudder will lack authority at low speed.) X-Plane can apply the left toe brake for you when you apply a lot of left rudder to help you turn.

In previous versions of X-Plane, this automatic toe-brake behavior was automatically applied based on some rules that Austin coded into X-Plane. When they worked, they really helped (and we know they sometimes worked because when we removed some of them in 11.30 we got bug reports), but at other times they weren’t tuned properly for a particular aircraft.

Starting in X-Plane 11.30 release candidate 1, aircraft authors can now explicitly control whether toe brakes are auto-applied for users without hardware, and if so, how aggressively. This control is auto-populated for older aircraft with the choices X-Plane 11.26 and earlier would have made, so you shouldn’t see a change in older aircraft behavior. The aircraft updating guide has the full details.

I believe that changes to these automatic rules may have been responsible for changes in third party aircraft ground handling in late 11.30 betas; hopefully with the new code, we should see complete compatibility.

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