[Beowulf] [upgrade strategy] Intel CPU design bug & security flaw - kernel fix imposes performance penalty

[Christopher Samuel]

On 05/01/18 10:48, Jörg Saßmannshausen wrote:

> What I would like to know is: how about compensation? For me that is
> the same as the VW scandal last year. We, the users, have been
> deceived.

I think you would be hard pressed to prove that, especially as it seems
that pretty much every mainstream CPU is affected (Intel, AMD, ARM, Power).

> Specially if the 30% performance loss which have been mooted are not
> special corner cases but are seen often in HPC. Some of the chemistry
> code I am supporting relies on disc I/O, others on InfiniBand and
> again other is running entirely in memory.

For RDMA based networks like IB I would suspect that the impact will be
far less as the system calls to set things up will be impacted but that
after that it should be less of an issue (as the whole idea of RDMA was
to get the kernel out of the way as much as possible).

But of course we need real benchmarks to gauge that impact.

Separating out the impact of various updates will also be important,
I've heard that the SLES upgrade to their microcode package includes
disabling branch prediction on AMD k17 family CPUs for instance.

All the best,
Chris
-- 
  Chris Samuel  :  http://www.csamuel.org/  :  Melbourne, VIC