CPU Usage Differences After Applying Meltdown Patch at Epic Games • Hacker News Board

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#191

Post by anonacct37 » Sat, Jan 06, 2018, 5:07 PM UTC

Waterluvian wrote: post #166

forgotpw2018 wrote: post #153

Earlier quoted context omitted.

Intel's PR dept is in overdrive, but the truth about this vulnerability is that it's essentially worst-case. It really only affects workloads where high performance is important. The average user might not see an impact but if you need fast IO God help you. The solution is to 'make less syscalls' but the problem is that syscalls have always been slow and the people making a lot of them are only doing so because they…

Isn't that like saying that it turns out this car we sold can only do 150, not 200. But it's okay because most of you never drive above 80 anyways. You're right. Most people who just surf the Netflix and download the YouTubes will not notice. But it's still a form of fraud, even to those who never max out CPU. I think fraud is a strong word knowing that this wasn't intentional. But they sold a lesser product than the…

I think people are underestimating how bad webapps are. I do... a lot of computing and by far the most CPU intensive applications on my computer are webviews. Either Gmail in chrome or slack. I'm actually going to be upgrading my laptop soon because slack+3 organizations crushes my laptop.

Do you think browser vendors have been pushing JIT research forward, investing in webasm, and building things like servo because websites are so fast and light on CPU?

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#192

Post by johnbellone » Sat, Jan 06, 2018, 5:07 PM UTC

lazyjones wrote: post #154

Those who have looked at the patches in detail: does it treat older generation CPUs differently than 7th gen? The Paper authors who wrote the KAISER patch expected much worse performance on older CPUs due to implementation issues... Unfortunately, Epic Games don't provide any details about their CPUs AFAICT.

They did mention that they were using a cloud provider. But that’s about it.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#193

Post by tgb » Sat, Jan 06, 2018, 5:08 PM UTC

dogma1138 wrote: post #115

tgb wrote: post #62

Earlier quoted context omitted.

Since they describe this as log-in issues, should we expect that to be a server using lots of UDP? Or do you think that the log-in service is hemmed in by the load on the game servers?

No, login in Fortnite is over 443 and it uses normal HTTPS. It also uses HTTPs to load a lot of other data such as server data, friends list, chat etc. Unreal Engine comes with a version of chromium built in which is used for many in game things like social tabs, news, and in game purchases these all work over HTTP/S. Game data is sent over 5222 TCP.

Right, that's what I was guessing and am not sure why I was downvoted when everyone is confirming that contrarian's post doesn't really make sense since UDP isn't very relevant here.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#194

Post by userbinator » Sat, Jan 06, 2018, 5:10 PM UTC

toomuchtodo wrote: post #136

drawnwren wrote: post #76

Earlier quoted context omitted.

This is a horrible approach to security. If you only secure against attacks you expect, you're gonna have a bad time.

Security is about risk mitigation. You cannot derisk entirely, so you make tradeoffs. Without knowing all of the parameters, it’s disingenuous to say it’s a horrible approach to security. The most secure computer is powered off, enclosed in concrete 6 feet below the surface of the earth. It is not very useful though.

Very much this. In the real world, basically no one will make their house entirely bulletproof and never go outside just because of the possibility that someone could shoot them. Everyone knows that could happen, but is fine with the risk.

"100% secure" is unattainable, and to attempt to achieve it to the exclusion of all other concerns is probably a very bad idea.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#195

Post by yborg » Sat, Jan 06, 2018, 5:10 PM UTC

Abishek_Muthian wrote: post #60

If it's helpful, Our Node.js, MongoDB, Python servers all with significant network traffic didn't have any measurable impact after KPTI patches on Amazon Linux on T2.medium(burst), M4.large, T2.large(burst) respectively. Our impact is lesser than the figures suggested by redhat's advisory - https://access.redhat.com/articles/3307751

"Significant network traffic" tells me almost nothing, that's a totally subjective description and you don't describe your workload at all.

A back-end MMO game infrastructure server I have some understanding of in terms of the kind of load it is handling.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#196

Post by Retric » Sat, Jan 06, 2018, 5:10 PM UTC

jimmaswell wrote: post #189

dk1138 wrote: post #175

Earlier quoted context omitted.

If you bought a car that needed to go 60mph and a subsequent update to the car from the manufacturer for safety meant it could only go 30mph, there would be legal consequences. Of course you can't predict every contingency, but some of them you pay for.

Did Intel ever specifically 100% promise a certain performance in their advertising? Do they have contracts having such promises in them with vendors?

I have seen Intel post benchmarks that are no longer correct. So, yes.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#197

Post by cookiecaper » Sat, Jan 06, 2018, 5:11 PM UTC

drawnwren wrote: post #76

Darthy wrote: post #71

The Meltdown attack requires an attacker to have a piece of code executed on your server. Epic's servers are used for login, where people send you data, and for game logic, where people also just send you data like "player x moved his avatar here, player y shoots etc". If all the server does is execute the code which Epic wrote themselves and already trust, why would it need to apply the Meltdown patch?

This is a horrible approach to security. If you only secure against attacks you expect, you're gonna have a bad time.

Some things are just not applicable. There's no point adding another padlock to the outside wall of Fort Knox. If untrusted users don't send instructions to the same physical CPU that you're using, Meltdown/Spectre are not relevant.

I also think that we need more information before we really see the long-term performance impact here. First, the patches will likely be optimized over time. Second, I am not sure that PTI needs to be run within guest kernels if the host already has the mitigation (effectively creating a double-hit from PTI in both the guest and host kernel), or that even if PTI is needed in both kernels now, that it will be needed long-term. We also need to figure out what type of Spectre mitigations need to be performed within the guest if the host system has the new microcode that selectively disables branch prediction.

The short answer is that it's going to take another 4-6 weeks before even the kernel devs have a firm grasp of what's useful/necessary to mitigate this and for things to settle into place, as Greg K-H blogged about earlier. At that point, we should have a more realistic perspective on the long-term performance impact.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#198

Post by dogma1138 » Sat, Jan 06, 2018, 5:13 PM UTC

Demiurge wrote: post #158

dogma1138 wrote: post #100

Earlier quoted context omitted.

The majority of online games use TCP these days with good prediction it’s more reliable than UDP.

Latency is more important than reliability for online gaming because the world state instantly gets stale. Instead of retransmit you want latest snapshot. I'd be curious to find out in what online games that is not the case.

Latency isn’t an issue today what so ever, it’s not like UDP also has a magical lower latency it had in the past because of smaller packets and slower computers but today?

Online games work today with fixed ticks and polling usually at half of full frame rate which means that the server updates and polls the client 30 or 60 times a second or any other even multiplier of the expected synced frame rate.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#199

Post by dogma1138 » Sat, Jan 06, 2018, 5:14 PM UTC

jbg_ wrote: post #138

dogma1138 wrote: post #115

Earlier quoted context omitted.

No, login in Fortnite is over 443 and it uses normal HTTPS. It also uses HTTPs to load a lot of other data such as server data, friends list, chat etc. Unreal Engine comes with a version of chromium built in which is used for many in game things like social tabs, news, and in game purchases these all work over HTTP/S. Game data is sent over 5222 TCP.

Out of interest, do you know if the game data uses XMPP or if it just uses the same port?

5222 is pretty much used for all Epyc games I don’t think that I has anything to do with XMMP tho.

Re: CPU Usage Differences After Applying Meltdown Patch at Epic Games

#200

Post by AFNobody » Sat, Jan 06, 2018, 5:15 PM UTC

sillysaurus3 wrote: post #168

forgotpw2018 wrote: post #132

Huge real world performance impact, they didn't say how much but it looks like close to 100%. I smell a class action lawsuit coming.

Hopefully not. Lawsuits are a fine way to stifle innovation. Imagine how hard it would be to push through any idea at Intel. No one saw this coming. Things happen. It's impossible to predict every contingency. They acted in good faith. Also, heh, users are funny: "all other games i have work fin by the way so there must be a problem whit fortnite."

> They acted in good faith.

The PR spin and misdirection games isn't in good faith which completely demolishes this line of defense.