Looking At The Linux Performance Two Years After Spectre / Meltdown Mitigations

[tildearrow]

Honestly, Michael: This kind of content should only be available to paying subscribers for the first week after publication.

Are you trying to turn this into LWN?

[betam4x]

Should have thrown some AMD CPUs in there just to set everyone off.

[birdie]

NoScript + "mitigations=off" for the Win. Don't run untrusted software? No need to lose all your performance.

1. Too many websites are unusable without JS, even the phoronix forums.
2. When you don't enable JS, even a PC from 20 years ago is fast enough to browse the web.

[mitch074]

Great testing. Does show how badly ignorant we've been to hw cheating.

I'd like to see how AMD has faired here, with Zen1-3 and EPYC + TR chips.

No need : it's been done already, on Phoronix, here : https://www.phoronix.com/scan.php?pa...-spectre&num=1

Zen 1 is almost identical here to Zen+, which included some optimizations in RAM access and cache latency, but absolutely no core redesign. All in all, Ryzen chips weren't impacted much on average.

[S.Pam]

Great testing. Does show how badly ignorant we've been to hw cheating.

I'd like to see how AMD has faired here, with Zen1-3 and EPYC + TR chips.

[hotaru]

still no tests with all mitigations enabled (rather than just the default ones)?

[xnor]

Guys, Intel did not fix these defects by fixing the hardware design. That would have required a major redesign.
Low-hanging fruits could have been fixed in actual hardware but the rest is just the same broken CPUs shipped with "fixes" (workarounds) in the firmware.

[Michael]

I wouldn't be so fast to jump to that conclusion. For that we'd have to benchmark comparable chips such as i9-9980XE against i9-10980XE. Some of the HW fixes seem to help without hurting the performance, see the ctx_clock test for instance. Robbing the user of the opportunity to get some performance back by switching the mitigations off seems rather idiotic.

@Michael: Would you consider to benchmark the effect of HW mitigations on the Cascade Lake chips, assuming you have the hardware to benchmark it on?

Unfortunately I don't have a 9980XE thus why that testing hasn't happened. Nor any extra funds just to buy an idetical chip in the 9000 series if it has hardware mitigations on certain steppings.

[MadCatX]

Well if you look at the bar graphs some of those results show the newer chip with hardware mitigations performing much worse than the chips without hardware mitigations. Even though the software mitigations don't much affect the result, the result is that some of those results for chips with hardware mitigations much worse than the chips without hardware mitigations even when using the software mitigations.

Just look at some of the GEGL, GIMP, and OSbench results.... The software mitigations don't much affect that one chip, but that one chip is performing much worse than the comparable older chip. I'd even go so far as to say the hardware mitigations on the newer chip are impacting performance much worse than the software mitigations are on the comparable older chip.

I wouldn't be so fast to jump to that conclusion. For that we'd have to benchmark comparable chips such as i9-9980XE against i9-10980XE. Some of the HW fixes seem to help without hurting the performance, see the ctx_clock test for instance. Robbing the user of the opportunity to get some performance back by switching the mitigations off seems rather idiotic.

@Michael: Would you consider to benchmark the effect of HW mitigations on the Cascade Lake chips, assuming you have the hardware to benchmark it on?

[rastersoft]

If I'm using a desktop computer just for desktop stuff, no server, and only with software from debian repositories, is it safe to disable all these mitigations? Or maybe only some? (and which ones?)

Thanks.