KAISER: hiding the kernel from user space [LWN.net]

KAISER: hiding the kernel from user space

Posted Nov 15, 2017 5:54 UTC (Wed) by jreiser (subscriber, #11027)
Parent article: KAISER: hiding the kernel from user space

(CR3 manipulation) add a few hundred cycles to a syscall or interrupt. That's a couple L3 cache misses [CAS latency on SDRAM has been ~60ns for decades] which probably is tolerable on a syscall. But hundreds of cycles is horrible for an interrupt. [33MHz is a common bus clock, so just generating an interrupt already requires an average latency of ~15ns.] Some architectures have a special interrupt context (and/or separate small locked caches) exactly for this reason.

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KAISER: hiding the kernel from user space

Posted Nov 15, 2017 15:39 UTC (Wed) by hansendc (subscriber, #7363) [Link] (1 responses)

Interrupts are already a small number of thousands cycles, even for a quick one. The entry plus IRET costs alone probably eclipse the (new) CR3 manipulation cost. So, while this CR3 manipulation makes things worse, it does not fundamentally change the speed of an interrupt.

KAISER: hiding the kernel from user space

Posted Dec 9, 2018 15:58 UTC (Sun) by dembego3 (guest, #129120) [Link]

Thank you for caring for my safety:-)