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Netflix warning over Intel’s latest Meltdown fix that could cause CPU latency spikes of 8,000 per cent

Intel’s operating-system level patch for the Meltdown CPU security flaw could cause a serious increase in latency issues, if the patch for Linux is any guide, according to research conducted by Netflix. 

It suggests that users could experience an 8,000 per cent rise in CPU latency after applying the Meltdown patches.

Brendan Gregg, who is part of the team that ensures that Netflix performs as planned, says that the Linux fix causes a huge strain on the CPU leading to the “largest kernel performance regressions I’ve ever seen”.

The technique is called Kernel Page Table Isolation (KPTI) and does pretty much what it says – it makes sure that the page tables for users are different for the ones used by the machine.

Netflix is estimated to have a fairly low level of latency rise – between 0.1 and six per cent. But others could see a huge rise, in the hundreds or into those thousands.

“Where you are on that spectrum depends on your syscall and page fault rates, due to the extra CPU cycle overheads, and your memory working set size, due to TLB flushing on syscalls and context switches.”

Meltdown and Spectre have primarily affected Intel chips at a structural level, but all chip makers and operating systems are having to ensure that they are immune.

Intel has warned from the outset that a performance drop was likely, but Linux creator Linus Torvalds has already made clear that he thinks that the Intel mitigations are “very much part of the whole ‘this is complete garbage’ issue.”

He added: “WHAT THE F*CK IS GOING ON? And that’s actually ignoring [a] much _worse_ issue, namely that the whole hardware interface is literally mis-designed by morons.”

Google has offered its own patch for Spectre, known as Reptoline, which it claims will have no or at least negligible impact on performance. However, Meltdown is the bigger problem, and that’s the one causing the bigger headache to fix without borking everyone’s machines.

As yet, neither Meltdown or Spectre are thought to have affected anyone’s machines in a real-world situation, but the fixes could have an impact on hardware buyers this year as they wait for CPU makers – Intel in particular, as the most affected – to design-out both flaws from their products. 

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