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From: Marc Zyngier <maz@kernel.org>
To: Jingyi Wang <wangjingyi11@huawei.com>
Cc: drjones@redhat.com, kvm@vger.kernel.org,
	kvmarm@lists.cs.columbia.edu, eric.auger@redhat.com,
	wanghaibin.wang@huawei.com, yuzenghui@huawei.com
Subject: Re: [kvm-unit-tests PATCH v3 00/10] arm/arm64: Add IPI/LPI/vtimer latency test
Date: Tue, 11 Aug 2020 08:49:08 +0100
Message-ID: <b175763e4f4f08ecdae46e6e87b0bc81@kernel.org> (raw)
In-Reply-To: <54de9edf-3cca-f968-1ea8-027556b5f5ff@huawei.com>

On 2020-08-11 02:48, Jingyi Wang wrote:
> Hi Marc,
> 
> On 8/5/2020 8:13 PM, Marc Zyngier wrote:
>> On 2020-08-05 12:54, Jingyi Wang wrote:
>>> Hi all,
>>> 
>>> Currently, kvm-unit-tests only support GICv3 vLPI injection. May I 
>>> ask
>>> is there any plan or suggestion on constructing irq bypass mechanism
>>> to test vLPI direct injection in kvm-unit-tests?
>> 
>> I'm not sure what you are asking for here. VLPIs are only delivered
>> from a HW device, and the offloading mechanism isn't visible from
>> userspace (you either have an enabled GICv4 implementation, or
>> you don't).
>> 
>> There are ways to *trigger* device MSIs from userspace and inject
>> them in a guest, but that's only a debug feature, which shouldn't
>> be enabled on a production system.
>> 
>>          M.
> 
> Sorry for the late reply.
> 
> As I mentioned before, we want to add vLPI direct injection test
> in KUT, meanwhile measure the latency of hardware vLPI injection.
> 
> Sure, vLPI is triggered by hardware. Since kernel supports sending
> ITS INT command in guest to trigger vLPI, I wonder if it is possible

So can the host.

> to add an extra interface to make a vLPI hardware-offload(just as
> kvm_vgic_v4_set_forwarding() does). If so, vgic_its_trigger_msi()
> can inject vLPI directly instead of using LR.

The interface exists, it is in debugfs. But it mandates that the
device exists. And no, I am not willing to add an extra KVM userspace
API for this.

The whole concept of injecting an INT to measure the performance
of GICv4 is slightly bonkers, actually. Most of the cost is paid
on the injection path (queuing a pair of command, waiting until
the ITS wakes up and generate the signal...).

What you really want to measure is the time from generation of
the LPI by a device until the guest acknowledges the interrupt
to the device itself. and this can only be implemented in the
device.

         M.
-- 
Jazz is not dead. It just smells funny...

  reply index

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-31  7:42 Jingyi Wang
2020-07-31  7:42 ` [kvm-unit-tests PATCH v3 01/10] arm64: microbench: get correct ipi received num Jingyi Wang
2020-07-31  7:42 ` [kvm-unit-tests PATCH v3 02/10] arm64: microbench: Generalize ipi test names Jingyi Wang
2020-07-31  7:42 ` [kvm-unit-tests PATCH v3 03/10] arm64: microbench: gic: Add ipi latency test for gicv4.1 support kvm Jingyi Wang
2020-07-31  7:42 ` [kvm-unit-tests PATCH v3 04/10] arm64: its: Handle its command queue wrapping Jingyi Wang
2020-07-31  7:42 ` [kvm-unit-tests PATCH v3 05/10] arm64: microbench: its: Add LPI latency test Jingyi Wang
2020-07-31  7:42 ` [kvm-unit-tests PATCH v3 06/10] arm64: microbench: Allow each test to specify its running times Jingyi Wang
2020-07-31  7:42 ` [kvm-unit-tests PATCH v3 07/10] arm64: microbench: Add time limit for each individual test Jingyi Wang
2020-08-01 16:13   ` Andrew Jones
2020-07-31  7:42 ` [kvm-unit-tests PATCH v3 08/10] arm64: microbench: Add vtimer latency test Jingyi Wang
2020-08-01 16:22   ` Andrew Jones
2020-07-31  7:42 ` [kvm-unit-tests PATCH v3 09/10] arm64: microbench: Add test->post() to further process test results Jingyi Wang
2020-08-01 17:03   ` Andrew Jones
2020-07-31  7:42 ` [kvm-unit-tests PATCH v3 10/10] arm64: microbench: Add timer_post() to get actual PPI latency Jingyi Wang
2020-07-31 12:01 ` [kvm-unit-tests PATCH v3 00/10] arm/arm64: Add IPI/LPI/vtimer latency test Andrew Jones
2020-08-03  2:15   ` Jingyi Wang
2020-08-01 17:40 ` Andrew Jones
2020-08-05 11:54 ` Jingyi Wang
2020-08-05 12:13   ` Marc Zyngier
2020-08-11  1:48     ` Jingyi Wang
2020-08-11  7:49       ` Marc Zyngier [this message]
2020-08-17  1:46         ` Jingyi Wang
2020-08-17  8:26           ` Marc Zyngier

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