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Linux Developers Discuss Flushing L1 Cache On Context Switches In Light Of Vulnerabilities
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Originally posted by Danny3 View PostOh come on, not another performance crippling change. ....
In my opinion. do all the security enhancement you want, but stop enabling them by default !Last edited by CommunityMember; 19 March 2020, 02:14 PM.
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As long as something like this can be disabled for AMD CPUs, then I would have no issues with it. Intel have long wanted to bring in 'fixes' that make performance poor on all platforms, so it doesn't look as bad for them. Other processors that don't have flaws shouldn't have to suffer the performance degradation just to make Intel work better. If something is an Intel-only issue, it should only affect them.
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Originally posted by Dr_ST View PostI'm a computing researcher (in biology) and for many years I'm told that in large computing centers they always disable HT (since 2007-8 or so)
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I have not looked into the details of the L1 cache flush pr. context, but the first impression is that this is a GLOBAL feature. The first thing that crosses my mind is , why not set this on a per. cpu / socket basis so that you effectively have a safe and/or unsafe scheduling domain. This means that you could have set the processor affinity for unsecure programs to run on the CPU group that flushes the L1 cache while things that you trust could run without mitigations on other CPU's. Servers today usually have a handful of CPU cores to play with , and even if you did not have that many CPU's to pay with you could probably reduce some of the performance impact by modifying the scheduler to group programs safe/unsafe so that you would not have to flush the L1 cache as often...
http://www.dirtcellar.net
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Originally posted by CommunityMember View Post
Depending on the specific implementation, HT can have substantial performance disadvantages in some computationally intensive applications (as a thread swap results in the flushing of caches being used by other threads). That is obviously something very targeted to specific codes, but the HPC market has those specific codes, and most competent HPC computing centers have run the tests for their codes to know what (HT on, HT off) is better.
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