linux-kernel - Re: [RFC PATCH 0/2] Adjust CFS loadbalance to adapt QEMU CPU topology.

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Message-ID: <20230721091106.GD3630545@hirez.programming.kicks-ass.net>
Date:   Fri, 21 Jul 2023 11:11:06 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Kenan.Liu" <Kenan.Liu@...ux.alibaba.com>
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, luoben@...ux.alibaba.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] Adjust CFS loadbalance to adapt QEMU CPU
 topology.

On Fri, Jul 21, 2023 at 10:58:50AM +0800, Kenan.Liu wrote:

> > > As the current kernel scheduler
> > > implementation, hyperthread with an even ID number will be picked up in a much
> > > higher probability during load-balancing and load-deploying.
> > How so?
> 
> 
> The SMT topology in qemu native x86 CPU model is (0,1),…,(n,n+1),…,
> but nomarlly seen SMT topo in physical machine is like (0,n),(1,n+1),…,
> n means the total core number of the machine.

That is only common on Intel hardware, AMD (and some Intel) will in fact
enumerate SMT like Qemu does.