linux-kernel - 答复: [PATCH] KVM: Consider SMT idle status when halt polling

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Date:   Thu, 22 Jul 2021 12:16:53 +0000
From:   "Li,Rongqing" <lirongqing@...du.com>
To:     Wanpeng Li <kernellwp@...il.com>
CC:     Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        kvm <kvm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: 答复: [PATCH] KVM: Consider SMT idle status when halt polling

> > > SMT siblings share caches and other hardware, halt polling will
> > > degrade its sibling performance if its sibling is busy
> >
> > Do you have any real scenario benefits? As the polling nature, some
> > cloud providers will configure to their preferred balance of cpu usage
> > and performance, and other cloud providers for their NFV scenarios
> > which are more sensitive to latency are vCPU and pCPU 1:1 pin，you
> > destroy these setups.
> >
> >     Wanpeng
> 


Run a copy (single thread) Unixbench, with or without a busy poll program in its SMT sibling,  and Unixbench score can lower 1/3 with SMT busy polling program

Can this case show this issue?

-Li 


> True, it benefits for our real scenario.
> 
> this patch can lower our workload compute latency in our multiple cores VM
> which vCPU and pCPU is 1:1 pin, and the workload with lots of computation and
> networking packets.
> 
> -Li