From: Peter Zijlstra <peterz@infradead.org>
To: Masanori Misono <m.misono760@gmail.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>,
Paolo Bonzini <pbonzini@redhat.com>,
Rohit Jain <rohit.k.jain@oracle.com>,
Ingo Molnar <mingo@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC 0/1] Make vCPUs that are HLT state candidates for load balancing
Date: Wed, 26 May 2021 16:43:03 +0200 [thread overview]
Message-ID: <YK5ed8ixweIAsvlL@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210526133727.42339-1-m.misono760@gmail.com>
On Wed, May 26, 2021 at 10:37:26PM +0900, Masanori Misono wrote:
> is_vcpu_preempted() is also used in PV spinlock implementations to mitigate
> lock holder preemption problems,
It's used to abort optimistic spinners.
> etc. A vCPU holding a lock does not do HLT,
Optimistic spinning is actually part of mutexes and rwsems too, and in
those cases we might very well end up in idle while holding the lock.
However; in that case the task will have been scheduled out and the
optimistic spin loop will terminate due to that (see the ->on_cpu
condition).
> so I think this patch doesn't affect them.
That is correct.
> However, pCPU may be
> running the host's thread that has higher priority than a vCPU thread, and
> in that case, is_vcpu_preempted() should return 0 ideally.
No, in that case vcpu_is_preempted() really should return true. There is
no saying how long the vcpu is gone for.
next prev parent reply other threads:[~2021-05-26 14:43 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-26 13:37 [PATCH RFC 0/1] Make vCPUs that are HLT state candidates for load balancing Masanori Misono
2021-05-26 13:37 ` [PATCH RFC 1/1] KVM: x86: Don't set preempted when vCPU does HLT VMEXIT Masanori Misono
2021-05-26 14:43 ` Peter Zijlstra [this message]
2021-05-26 14:49 ` [PATCH RFC 0/1] Make vCPUs that are HLT state candidates for load balancing Peter Zijlstra
2021-05-26 16:15 ` Sean Christopherson
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