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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>,
	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
Date: Mon, 10 Jun 2019 18:11:00 -0700	[thread overview]
Message-ID: <20190611011100.GB24835@linux.intel.com> (raw)
In-Reply-To: <20190610143420.GA6594@flask>

On Mon, Jun 10, 2019 at 04:34:20PM +0200, Radim Krčmář wrote:
> 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.)

Tangetially related to splitting PV IPI hypercalls, are there any major
hurdles to supporting shorthand?  Not having to generate the mask for
->send_IPI_allbutself and ->kvm_send_ipi_all seems like an easy to way
shave cycles for affected flows.

  reply	other threads:[~2019-06-11  1:11 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-30  1:05 Wanpeng Li
2019-05-30  1:05 ` [PATCH v3 1/3] KVM: X86: " Wanpeng Li
2019-05-30  1:05 ` [PATCH v3 2/3] KVM: X86: Implement PV sched yield hypercall Wanpeng Li
2019-06-10 14:17   ` Radim Krčmář
2019-06-11  8:47     ` Wanpeng Li
2019-05-30  1:05 ` [PATCH v3 3/3] KVM: X86: Expose PV_SCHED_YIELD CPUID feature bit to guest Wanpeng Li
2019-06-10  5:58 ` [PATCH v3 0/3] KVM: Yield to IPI target if necessary Wanpeng Li
2019-06-10 14:34 ` Radim Krčmář
2019-06-11  1:11   ` Sean Christopherson [this message]
2019-06-11  1:45     ` Wanpeng Li
2019-06-11  1:48       ` Nadav Amit
2019-06-11 10:02         ` Wanpeng Li
2019-06-11 16:57           ` Nadav Amit
2019-06-12  1:18             ` Wanpeng Li
2019-06-12  1:37               ` Nadav Amit
2019-06-28  9:12                 ` Wanpeng Li
2019-06-28  9:18                   ` Wanpeng Li
2019-06-11 10:26   ` Wanpeng Li

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