2 ms·
As syscalls run more code and access more data they can increase TLB pressure in the same way the increase general cache pressure, but syscalls per-se (outside
by gpderetta 3y ago
As syscalls run more code and access more data they can increase TLB pressure in the same way the increase general cache pressure, but syscalls per-se (outside of things like munmap) don't typically invalidate the TLB as the mapping is not changed on an user-space kernel-space transiation, only the access right (there were exceptions like the brief period when people where running with full 4GB user address space on 32bits cpu).
- panzi 3y ago> but syscalls per-se (outside of things like munmap) don't typically invalidate the TLB as the mapping is not changed on an user-space kernel-space transiation, only the access right Isn't that exactly what changed for the Meltdown/Spectre mitigations? That it is invalidated now?
- gpderetta 3y agoI think you are referring to KTPI, but a) it might not be needed on recent CPUs that had meltdown-like issues patched, and b) in any case on CPUs that can tag pages with process identifiers (most of them these days), it can avoid TLB flushes most of the time. But I don't claim any specific knowledge of on these mitigations.