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Bisected: The Unfortunate Reason Linux 4.20 Is Running Slower

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  • Bisected: The Unfortunate Reason Linux 4.20 Is Running Slower

    Phoronix: Bisected: The Unfortunate Reason Linux 4.20 Is Running Slower

    After running a lot of tests and then bisecting the Linux 4.20 kernel merge window, the reason for the significant slowdowns in the Linux 4.20 kernel for many real-world workloads is now known...

    http://www.phoronix.com/vr.php?view=27092

  • duby229
    replied
    Originally posted by L_A_G View Post

    That was the situation when the first white papers and proof-of-concept attacks were published, since then we've learned that the situation isn't quite so rosy for AMD or ARM-based CPUs.

    Intel, being the dominant player in the market, is obviously what security researchers aim for and testing to see if the exploits work on AMD and ARM is something they may or may not do after they've found the issue on Intel and got the proof-of-concept working. With the latest set of speculative execution vulnerabilities, published only last week, they didn't even test them on AMD as they simply didn't have the hardware lying around.

    Don't get me wrong, Intel definitely has cut more corners than AMD, but having been and to some extent continuing to be the dominant player in the market they're obviously going to be under more scrutiny than anyone else. This additional scrutiny will obviously make the situation look more lopsided than it actually is.
    Yeah, but the attitude you purvey about these researchers is just so ignorant and stupid because it doesn't reflect reality at all. If these researchers do in fact think like you describe, and somehow in my gut feelings I doubt that very much, then they can't possibly know for sure.

    Leave a comment:


  • L_A_G
    replied
    Originally posted by TemplarGR View Post
    AMD is only *realistically* vulnerable to the milder Spectre v1 variant.
    That was the situation when the first white papers and proof-of-concept attacks were published, since then we've learned that the situation isn't quite so rosy for AMD or ARM-based CPUs.

    Intel, being the dominant player in the market, is obviously what security researchers aim for and testing to see if the exploits work on AMD and ARM is something they may or may not do after they've found the issue on Intel and got the proof-of-concept working. With the latest set of speculative execution vulnerabilities, published only last week, they didn't even test them on AMD as they simply didn't have the hardware lying around.

    Don't get me wrong, Intel definitely has cut more corners than AMD, but having been and to some extent continuing to be the dominant player in the market they're obviously going to be under more scrutiny than anyone else. This additional scrutiny will obviously make the situation look more lopsided than it actually is.
    Last edited by L_A_G; 11-19-2018, 05:54 AM.

    Leave a comment:


  • carewolf
    replied
    Originally posted by ryao View Post
    1. AMD is vulnerable to Spectre v2.
    Only theoretically, not practically.. Which makes a huge difference in what kind of mitigations are warranted

    Originally posted by ryao View Post
    2. This patch is written in a way that should apply this mitigation to AMD hardware, whether it needs further mitigations or not.
    No, it it is written in a way where it COULD be applied to AMD hardware(*), but shouldn't necessarily, and isn't.

    Originally posted by ryao View Post
    3. Reports contradict #2.
    Not sure what you are talking about. You are contradicting yourself so much it is hard to keep track.

    * Note, when I repeat your term "AMD hardware" here, I mean Zen. Older AMD chips have indirect branch predicators more similar to Intels and are just as vulnerable. Only the latest Zen architectures have a newer design, that is effectively immune unless someone sets up specific circumstances, or a new trick is discovered.
    Last edited by carewolf; 11-18-2018, 07:32 PM.

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  • ryao
    replied
    Originally posted by juanrga View Post

    I guess you missed recent research and my former post:
    I did not miss it. However, I only refer to Spectre v3 as Meltdown and AMD processors are reportedly immune to it,

    Leave a comment:


  • hotaru
    replied
    Originally posted by juanrga View Post

    I guess you missed recent research and my former post:
    that's a bit disingenuous, considering that neither of the two meltdown-type vulnerabilities that affect AMD processors can cross privilege boundaries, while meltdown itself can and three other meltdown-type vulnerabilities that can cross privilege boundaries affect Intel processors, but not AMD.

    Leave a comment:


  • duby229
    replied
    Originally posted by juanrga View Post

    I guess you missed recent research and my former post:
    They would have to demonstrate an exploit in order to debunk AMD's supposed immunity, which they did not do. No exploit in the literal sense means no exploit.

    Leave a comment:


  • juanrga
    replied
    Originally posted by ryao View Post
    They are invulnerable to a handful of them, such as meltdown.
    I guess you missed recent research and my former post:

    We also debunk implicit assumptions including that AMD processors are immune to Meltdown-type effects

    Leave a comment:


  • juanrga
    replied
    Originally posted by Michael View Post
    All of my AMD systems were tested with their latest BIOS releases.
    That doesn't imply that all the mitigations were enabled for them.

    Leave a comment:


  • Weasel
    replied
    Originally posted by ryao View Post
    It is linear, not exponential. Voltage increases are quadratic. The unfortunate reality that higher clock speeds are dependent on voltage increases makes it cubic-ish.
    Damn that's even worse than I thought then.

    Leave a comment:

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