Kernel page-table isolation merged

Posted Jan 2, 2018 22:32 UTC (Tue) by andresfreund (subscriber, #69562)
In reply to: Kernel page-table isolation merged by andresfreund
Parent article: Kernel page-table isolation merged

> > The change isn’t in Linus’s tree yet, so I guess we’ll have to wait and see, but if the performance impact is significant on Intel processors and Ryzen and EPYC aren’t affected it could spell a serious problem for Intel.

> I don't think it'll be that bad. The patchset has ASID / PCID support on capable hardware reducing the syscall overhead on capable hardware (apparently sandy bridge onwards).

Some numbers for postgres workloads that more likely to suffer (i.e. very short statements with plenty syscalls, rather than analytics workloads):
https://www.postgresql.org/message-id/20180102222354.qikj...

readonly pgbench (tpch-like), 16 clients, i7-6820HQ CPU (skylake):

pti=off:
tps = 236629.778328

pti=on:
tps = 220791.228297 (~0.93x)

pti=on, nopcid:
tps = 198959.801459 (~0.84x)

To get closer to the worst case, I've also measured:

pgbench SELECT 1, 16 clients, i7-6820HQ CPU (skylake):

pti=off:
tps = 420490.162391

pti=on:
tps = 350746.065039 (~0.83x)

pti=on, nopcid:
tps = 324269.903152 (~0.77x)

So yea, definitely not fun :(