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CPU Usage Differences After Applying Meltdown Patch at Epic Games

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

#211

Post by kazagistar »

ChildOfChaos wrote: post #186
bartread wrote: post #129

Earlier quoted context omitted.

Whilst I sympathise with your frustration, at least with Intel, I can't help feeling like you might be storing up bigger problems for yourself with this course of action.

I get what you are saying but right now there are no known exploits and with so much patching happening will there ever? These things are always over blown in the media and the reality is very little damage happens to the average user. It’s servers perhaps that are most at risk. Also I don’t do much on my Windows, mostly gaming, I run an iMac and boot into it only for certain tasks, so it’s extremely unlikely I will…

What do you mean "no known exploits"? The authors of the paper have an exploit that reads arbitrary system memory from a browser. And even after the meltdown patches, spectre "fixes" we have seen are only partial mitigation, and still potentially allow reading of passwords and third party cookies. But I guess if you want to wait til it's too late...

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

#212

Post by serf »

andrewaylett wrote: post #110
j1vms wrote: post #106

Maybe off-topic: Is formal verification viable anywhere in CPU logic design? Also, could any existing "CPU static analyzers" have caught the issue that caused Meltdown? Edit: It looks like the answer to the first is a definite yes.

Formal verification of what? You can only verify properties you've thought of, and no-one conceived of this particular 'feature' causing issues like this until now. So I don't think formal verification would have helped: if anyone was in a position to realise the issue was worth verifying, they'd have been able to raise it without formal verification too.

>You can only verify properties you've thought of, and no-one conceived of this particular 'feature' causing issues like this until now.

I've read for years about supposed insecurities with branch prediction -- it just wasn't shown practically. To say that it wasn't conceived of is a little off.

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

#213

Post by djsumdog »

forgotpw2018 wrote: post #153
Filligree wrote: post #142

Earlier quoted context omitted.

More than a doubling of CPU use, but for consistency's sake: The other percentages we've been offered have been in terms of performance reduction. We were told to expect a range of 5-30%; this is about 60%. Somewhere a sysadmin's hair has started smoldering.

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…

I wonder if we'll start seeing more userspace storage drivers because of this.

If anything, for big shops like this one, I wouldn't be surprised if we saw a move away from hosted providers (the "cloud" .. god I still hate it when people use that word), and return to co-located setups.

At least for people who need immediately performance needs, AMD might make a lot of short term sales right now.

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

#214

Post by nemothekid »

ChildOfChaos wrote: post #186
bartread wrote: post #129

Earlier quoted context omitted.

Whilst I sympathise with your frustration, at least with Intel, I can't help feeling like you might be storing up bigger problems for yourself with this course of action.

I get what you are saying but right now there are no known exploits and with so much patching happening will there ever? These things are always over blown in the media and the reality is very little damage happens to the average user. It’s servers perhaps that are most at risk. Also I don’t do much on my Windows, mostly gaming, I run an iMac and boot into it only for certain tasks, so it’s extremely unlikely I will…

What do you mean by “no known exploits”? There are several PoCs out, one of which is in JavaScript for meltdown.

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

#215

Post by mistercow »

[deleted] wrote: post #178
Waterluvian wrote: post #166

Earlier quoted context omitted.

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…

[deleted]

Is that remotely feasible? You're basically suggesting that Intel needs to refund or replace every PC and server CPU they've sold in the last five years.

The fdiv recall cost Intel almost half a billion dollars, and that was for a small subset of processors that most people didn't replace. Intel has a lot of assets, but replacing five years worth of CPUs might actually bankrupt them.

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

#216

Post by djsumdog »

chrisper wrote: post #157
pitaj wrote: post #137

Earlier quoted context omitted.

Why? This wasn't gross incompetence in processor design, this kind of attack is completely new. I don't see how a class action could apply here, by IANAL

If you know that your product is flawed, do you keep selling it or will you pull it from the shelves? To this date I can still buy broken Intel CPUs.... They knew about the flaw in June. Yet they still kept selling Coffee Lake CPUs. If my 8700k wouldn't still be significantly faster than Amd Ryzen (or I wouldn't have to also return the MB), I would have switched to an Amd in a heart beat.

To be fair to Intel, mitigating this type of issue isn't at all trivial. If it were, it could have been fixed in a microcode update. You can't rush a chip design for something as complicated as x86_64. There are long multi-year development cycles and tons of regression tests.

With this they need to add even more tests before they can start on attacking the issues with the design.

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

#217

Post by bschwindHN »

dogma1138 wrote: post #198
Demiurge wrote: post #158

Earlier quoted context omitted.

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.

I'm calling bullshit. TCP has to retransmit lost packets whereas UDP can keep on going without waiting for transmission. Ephemeral data like controller input or past game states can be ignored because that time has passed, while TCP is still trying its best to get the packets there in order and reliably.

Latency is still absolutely an issue. I play games from Japan with my friends in the states and I often have a ping of 140 ms or so. That is latency, and properly implemented games (Rocket League, for example) will deal with it using UDP among other techniques.

Slower paced games can still use TCP though because latency issues are less sensitive.

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

#218

Post by cthalupa »

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.

I believe PCID is supposed to help mitigate the performance impact from the KPTI changes.

Both the hardware and kernel have to support PCID

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

#219

Post by djsumdog »

fermienrico wrote: post #174
erdbeerkuchen wrote: post #111

The image didn't show up for me, here is a direct link for anyone with the same problem: https://lh6.googleusercontent.com/MwzsHRXQLVbmJ3pusNuGwn0ZQV...

Can someone explain what 1, 2 and 3 series in the plot means? What are we looking at? Why did one of them all of a sudden spiked?

Yea I hated that too. They put up a graph but with no key! Arg! The article said they updated one host, so I'm assuming the spike is from that one VM that got patched.

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

#220

Post by rdtsc »

pitaj wrote: post #137
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.

Why? This wasn't gross incompetence in processor design, this kind of attack is completely new. I don't see how a class action could apply here, by IANAL

Speculatively loading data across a protection boundary which is what happens in Meltdown can be argued to be incompetence or sneakiness. It certainly helps with benchmarks.

Moreover it would be hard to say "everyone is doing it" because it seems so far besides the latest ARM processors, most of the other CPU architectures don't do it.

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