Linus Torvalds reply about Meltdown and Spectre.


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# 1  
Linus Torvalds reply about Meltdown and Spectre.

Apologies if this is the wrong forum but...

...This is hard hitting stuff.

LKML: Linus Torvalds: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation
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# 2  
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As it is, the patches are COMPLETE AND UTTER GARBAGE.
.. for a only hypothetical problem.
# 3  
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Originally Posted by dodona
.. for a only hypothetical problem.
Perhaps, perhaps not; a hardware design problem that goes back decades just to get performance figures to sell their CPUs is more than bad to say the least - especially when the manufacturers knew about it.
Also, it can't be that hypothetical if it has been proven to work. It is the big/gigantic sytems that will be affected by these patches not so much the piffling little stuff like my MacBook Pro. I can handle a performance hit knowing about it now but can the big guns? <- Rhetorical!

But unless one has experience of writing kernels and OSes then one can't possibly know how difficult it is to create patches, (that will inherently give a performance hit just to _correct_ a deliberate manufacturing fault for profit), that will not slow things down too much.
# 4  
The x86 monoculture leads to risks like this.
See also --> OS monoculture...
# 5  
I read that with the 4.15 Kernel with build-in patches for the hypothetical problem comes with 15-30% performance loss. Immediately I thought 'wow, Intel, AMD and the hardware pushers will earn a lot of $'. I mean todays cpu is so fast that there isn't a need for a upgrade. However the hypothetical problem with the 15-30% performance loss is the need for an upgradeSmilie. Again everything comes down to $, and nothing else than $.Smilie
# 6  
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Originally Posted by dodona
I read that with the 4.15 Kernel with build-in patches for the hypothetical problem comes with 15-30% performance loss.
That's way overblown, because the performance loss happens during the switch between userspace and kernelspace. Sensible programs don't spend most of their time doing thousands of tiny system calls.

A 30% reduction in performance there is bad, but not the same as a 30% slower computer.
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