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CPU Usage Differences After Applying Meltdown Patch at Epic Games

epicgames.com

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

#291

Post by em3rgent0rdr »

burnte wrote: post #274
yborg wrote: post #195

Earlier quoted context omitted.

"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.

It tells us his workload is more network bound than computationally intensive.

More specifically, the meltdown patch primarily affect memory bound applications, not necessarily computations, although those usually overlap for CPU bound applications.

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

#292

Post by em3rgent0rdr »

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?

Your argument also applied to other circumstances where the computer only runs trusted code. For example a fully FLOSS software stack on home computer with JavaScript disabled in the browser.

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

#293

Post by em3rgent0rdr »

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.

Reminds me of Battlestar Galactica. The humans were so (wisely) fearful of the Cylons that their ship computers were not networked in anyway. For their risk/reward trade-off curve, the benefit from having computer networks were not worth the risk of the Cylons being able to compromise the entire ship. All communication was either verbal or done via fax printed to paper and so had to go through human intermediaries.

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

#294

Post by em3rgent0rdr »

Tuna-Fish wrote: post #169
arien wrote: post #74

Earlier quoted context omitted.

Aren't they still vulnerable to Spectre?

Yes to the bounds check violation version, so far no to the BTB poisoning version. The bounds check version only works inside a single process, so is only relevant when you run untrusted code within the same process as some private data (such as JS in a web browser). AMD claims that they believe that the way their branch predictor works effectively makes the BTB poisoning unusable, but there is no actual proof, and t…

Regarding branch predictor spoiling, if AMD doesn't update the branch predictor based off evaluation of branches the occurred along a speculative path, then the Spectre exploit (from my understanding that it trains the branch predictor using speculative code) won't be able to work.

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

#295

Post by toomuchtodo »

em3rgent0rdr wrote: post #293
toomuchtodo wrote: post #136

Earlier quoted context omitted.

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.

Reminds me of Battlestar Galactica. The humans were so (wisely) fearful of the Cylons that their ship computers were not networked in anyway. For their risk/reward trade-off curve, the benefit from having computer networks were not worth the risk of the Cylons being able to compromise the entire ship. All communication was either verbal or done via fax printed to paper and so had to go through human intermediaries.

Good catch!

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

#296

Post by Doxin »

jacquesm wrote: post #98
_wmd wrote: post #95

Earlier quoted context omitted.

I'd have presumed otherwise, but I'm not sure if you're understanding the API correctly.. it's not about sending multiple messages to the same destination, but to multiple destinations in a single call. The msg_hdr struct has room for specifying the target address. From userspace' perspective, even if the same data isn't being broadcast at every client, just building up a big array (perhaps while looping over the inp…

Yes, I understand the API correctly. Having implemented it once I think I have the basics down ;) But that said I was assuming that this would be in the context of multiple UDP messages sent from a game client to a game server.

The bottleneck generally isn't at the client side for games, The server has much more network traffic to handle. So even if this performance fix only works server-side that might be enough.
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