Subject: Re: [RFC 00/11]: powerKVM, release the compute power of secondary hwthread on host

From: Alexander Graf <[email-masked]>
Date: Tue, 18 Nov 2014 18:54:40 +0100

On 16.10.14 21:29, [email-masked] wrote:
> Nowadays, when running powerKVM(book3s, hv mode), we should make the secondary hwthread
> offline. Which means that if we run misc tsks other than dedicated KVM (e.g mix java and KVM),
> we will lose the compute power of the secondary hwthread on host env.

I'm personally more concerned about IO threads and the likes blocking
CPUs that could do actual work.

But really, IMHO this should just get fixed in hardware. The patch set
looks like quite a good addition of complexity to an already complex
problem - which means it will definitely break :).

Couldn't we just do something as simple as partition the system into SMT
and non-SMT cores? Then the user can just say "keep 2 cores in SMT mode"
and we would refuse to run KVM threads on those.

But then again we would bounce on these threads and increase latency on
entry if we happen to get scheduled there, so it's probably not a win
either.

I really don't have a good answer, except for "POWER8 wasn't designed
for this".

Alex