Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 10 Jun 2019 16:34:20 +0200
From:   Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
To:     Wanpeng Li <kernellwp@gmail.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH v3 0/3] KVM: Yield to IPI target if necessary
Message-ID: <20190610143420.GA6594@flask>
References: <1559178307-6835-1-git-send-email-wanpengli@tencent.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1559178307-6835-1-git-send-email-wanpengli@tencent.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

2019-05-30 09:05+0800, Wanpeng Li:
> The idea is from Xen, when sending a call-function IPI-many to vCPUs, 
> yield if any of the IPI target vCPUs was preempted. 17% performance 
> increasement of ebizzy benchmark can be observed in an over-subscribe 
> environment. (w/ kvm-pv-tlb disabled, testing TLB flush call-function 
> IPI-many since call-function is not easy to be trigged by userspace 
> workload).

Have you checked if we could gain performance by having the yield as an
extension to our PV IPI call?

It would allow us to skip the VM entry/exit overhead on the caller.
(The benefit of that might be negligible and it also poses a
 complication when splitting the target mask into several PV IPI
 hypercalls.)

Thanks.