The changes are too invasive (they will not backport cleanly), they are
not stable yet (there are still bugs being found in 4.14-rcX). The
performance implications are also not well-documented across the
platforms that we care about.
The opinion is that it is not practical or a good idea to pursue putting
this code back into old distributions, closing this.
** Changed in: intel
Status: New => Won't Fix
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https://bugs.launchpad.net/bugs/1718825
Title:
[Feature] Cristal Ridge: x86 Process Context IDentifiers (PCID)
support for OSV
Status in intel:
Won't Fix
Status in linux package in Ubuntu:
Incomplete
Bug description:
Description:
The mapping from virtual address to physical address will be stored in
someplace called TLB,
CPU need to occasionally flush TLB for different reasons, the flush will
impact all process address mapping,
with PCID support, the impact will be minimal, this will bring overcall
performance boost.
The commits comes from Andy Lutomirski(not Intel), which is quite recent, on
July 5 2017.
Part1:
660da7c9228f x86/mm: Enable CR4.PCIDE on supported systems
0790c9aad849 x86/mm: Add the 'nopcid' boot option to turn off PCID
cba4671af755 x86/mm: Disable PCID on 32-bit kernels
43858b4f25cf x86/mm: Stop calling leave_mm() in idle code
94b1b03b519b x86/mm: Rework lazy TLB mode and TLB freshness tracking
b0579ade7cd8 x86/mm: Track the TLB's tlb_gen and update the flushing algorithm
f39681ed0f48 x86/mm: Give each mm TLB flush generation a unique ID
Part2:
10af6235e0d3 x86/mm: Implement PCID based optimization: try to preserve old
TLB entries using PCID
Target Release: 17.10
Kernel: 4.14
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