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2nd January 2018, 23:53 | #1 | Link |
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Intel(?) bug incoming
https://www.reddit.com/r/sysadmin/co..._bug_incoming/
This is going to really hurt Intel dominance. Results in up to 30 percent performance loss. Does x264 or x265 happen to use syscalls? Probably not, right? |
3rd January 2018, 00:14 | #2 | Link |
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Any user-space application uses syscalls, mostly for memory (de)allocation and for I/O stuff, even though applications rarely do that directly. They use wrapper "system" userland-libraries, such as glibc (Linux) or kernel32 (Windows), which provide a "high level" interface to the functionality the application needs - and do the syscalls internally, where needed. The C Runtime adds yet another layer of abstraction between the application code and the underlying "system" libraries.
But, most important, unless the application is extremely I/O heavy, the syscall overhead is pretty much negligible. (And for applications that are very I/O heavy, the syscall overhead always has been a problem! That's why people came up with ideas like mapping the MMIO addresses into user-space and thus passing by the kernel and its drivers altogether )
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3rd January 2018, 06:16 | #3 | Link |
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My mistake. I guess what I meant to ask is how much it is relied upon for performance. I'm more of a hardware guy, but I figured that link would be useful.
https://www.phoronix.com/scan.php?pa...5-x86pti&num=2 X264 is uneffected it seems. Not sure about x265. |
3rd January 2018, 15:34 | #4 | Link | |
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For I/O-bound applications that do I/O in the "traditional" way, syscall overhead can become a bottleneck. And that's not a new problem at all! It just might get worse with KPTI (kernel page-table isolation) in place – on some older CPU's¹. At the moment everything is speculation, so let's wait for the kernel patches to actually role out. But, as far as x264 and x265 are concerned, you probably won't see a difference – except maybe with "ultra-fast" presets ¹ Newer CPU's support Process-Context Identifiers (PCIDs), which eliminates the need to flush the TLB and thus avoids most of the KPTI overhead. If you have one of those newer CPU's with support for PCIDs, you probably don't need to worry much.
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4th January 2018, 01:01 | #5 | Link | ||
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Apparently not really limited to Intel:
https://googleprojectzero.blogspot.d...with-side.html Quote:
Quote:
Furthermore, as far as I understand, KPTI (kernel page-table isolation), the fix that was discussed to cause some slow-down of syscalls, only fixes one of the three issues... Details: * https://spectreattack.com/spectre.pdf * https://meltdownattack.com/meltdown.pdf
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4th January 2018, 01:34 | #6 | Link | |
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The basic idea is described in the following excerpt (from the "Meltdown" paper):
Quote:
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4th January 2018, 02:34 | #7 | Link |
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Already on Linux kernel 4.14.11 which by default has PTI enabled and my /proc/cpuinfo reports "bugs : cpu_insecure". I do not see any slowdown in encoding speed here, neither in x264 nor in x265
Last edited by microchip8; 4th January 2018 at 02:45. |
5th January 2018, 08:52 | #8 | Link |
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The speed penalty for the patch is blown way out of proportion. The "30%" figure I've seen thrown around a lot is based on an artificial benchmark specifically designed to show this penalty and represents NO real world application I know of. x265 is bottlenecked computationally, and will not be effected.
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5th January 2018, 13:53 | #9 | Link | |
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EPYC will just destroy Xeon in these tasks after this security patch No wonder M$ decided to migrate Azure to EPYC.
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5th January 2018, 22:21 | #10 | Link |
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9th January 2018, 07:19 | #12 | Link |
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How Likely Is A Spectre/Meltdown Attack?
That title is what I googled, and this level-headed assessment came up:
https://www.networkworld.com/article...h-the-fud.html So, if true, a low chance of attack on an unpatched system, but still a chance, especially if an unsecured web browser can somehow be coerced into running the exploits. Otherwise, it's a lower consumer threat level than most other malwares, and sensible precautions could avoid it completely. Since there are emerging reports that OS+BIOS patched systems have their NVMe SSD performance absolutely clobbered (SATA performance is merely slapped, amongst other hits elsewhere), the question to patch or not to patch becomes more than an obvious security issue. It becomes one of whether you consider the threat serious enough to devalue your hardware, and do you apply only the OS Meltdown patch, or the Spectre BIOS patch as well. Last edited by WhatZit; 9th January 2018 at 07:28. Reason: Added NVMe Scary Story |
9th January 2018, 13:47 | #13 | Link | |
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2 of 3 benchs show no drop even on 4k, 1 bench has huge drop on every test, I'd blame that bench.
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12th January 2018, 18:14 | #14 | Link | |
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It's a pain to do in the cloud for high-touch craft encoding since uploading sources takes forever. But commercial content is already in the cloud. |
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