From: Jason Wang <jasowang@redhat.com>
To: "Zhu, Lingshan" <lingshan.zhu@intel.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
alex williamson <alex.williamson@redhat.com>,
pbonzini@redhat.com, sean.j.christopherson@intel.com,
wanpengli@tencent.com
Cc: "virtualization@lists.linux-foundation.org"
<virtualization@lists.linux-foundation.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
dan daly <dan.daly@intel.com>
Subject: Re: [PATCH 0/7] *** IRQ offloading for vDPA ***
Date: Thu, 16 Jul 2020 12:20:09 +0800 [thread overview]
Message-ID: <67c4c41d-9e95-2270-4acb-6f04668c34fa@redhat.com> (raw)
In-Reply-To: <a319cba3-8b3d-8968-0fb7-48a1d34042bf@intel.com>
On 2020/7/16 下午12:13, Zhu, Lingshan wrote:
>
>
> On 7/16/2020 12:02 PM, Jason Wang wrote:
>>
>> On 2020/7/16 上午11:59, Zhu, Lingshan wrote:
>>>
>>> On 7/16/2020 10:59 AM, Jason Wang wrote:
>>>>
>>>> On 2020/7/16 上午9:39, Zhu, Lingshan wrote:
>>>>>
>>>>>
>>>>> On 7/15/2020 9:43 PM, Jason Wang wrote:
>>>>>>
>>>>>> On 2020/7/12 下午10:52, Zhu Lingshan wrote:
>>>>>>> Hi All,
>>>>>>>
>>>>>>> This series intends to implement IRQ offloading for
>>>>>>> vhost_vdpa.
>>>>>>>
>>>>>>> By the feat of irq forwarding facilities like posted
>>>>>>> interrupt on X86, irq bypass can help deliver
>>>>>>> interrupts to vCPU directly.
>>>>>>>
>>>>>>> vDPA devices have dedicated hardware backends like VFIO
>>>>>>> pass-throughed devices. So it would be possible to setup
>>>>>>> irq offloading(irq bypass) for vDPA devices and gain
>>>>>>> performance improvements.
>>>>>>>
>>>>>>> In my testing, with this feature, we can save 0.1ms
>>>>>>> in a ping between two VFs on average.
>>>>>>
>>>>>>
>>>>>> Hi Lingshan:
>>>>>>
>>>>>> During the virtio-networking meeting, Michael spots two possible
>>>>>> issues:
>>>>>>
>>>>>> 1) do we need an new uAPI to stop the irq offloading?
>>>>>> 2) can interrupt lost during the eventfd ctx?
>>>>>>
>>>>>> For 1) I think we probably not, we can allocate an independent
>>>>>> eventfd which does not map to MSIX. So the consumer can't match
>>>>>> the producer and we fallback to eventfd based irq.
>>>>> Hi Jason,
>>>>>
>>>>> I wonder why we need to stop irq offloading, but if we need to do
>>>>> so, maybe a new uAPI would be more intuitive to me,
>>>>> but why and who(user? qemu?) shall initialize this process, based
>>>>> on what kinda of basis to make the decision?
>>>>
>>>>
>>>> The reason is we may want to fallback to software datapath for some
>>>> reason (e.g software assisted live migration). In this case we need
>>>> intercept device write to used ring so we can not offloading
>>>> virtqueue interrupt in this case.
>>> so add a VHOST_VDPA_STOP_IRQ_OFFLOADING? Then do we need a
>>> VHOST_VDPA_START_IRQ_OFFLOADING, then let userspace fully control
>>> this? Or any better approaches?
>>
>>
>> Probably not, it's as simple as allocating another eventfd (but not
>> irqfd), and pass it to vhost-vdpa. Then the offloading is disabled
>> since it doesn't have a consumer.
> OK, sounds like QEMU work, no need to take care in this series, right?
That's my understanding.
Thanks
>
> Thanks,
> BR
> Zhu Lingshan
>>
>> Thanks
>>
>>
next prev parent reply other threads:[~2020-07-16 4:20 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-12 14:52 [PATCH 0/7] *** IRQ offloading for vDPA *** Zhu Lingshan
2020-07-15 13:43 ` Jason Wang
[not found] ` <97032c51-3265-c94a-9ce1-f42fcc6d3075@intel.com>
2020-07-16 2:59 ` Jason Wang
[not found] ` <29ab6da8-ed8e-6b91-d658-f3d240543b29@intel.com>
[not found] ` <1e91d9dd-d787-beff-2c14-9c76ffc3b285@redhat.com>
[not found] ` <a319cba3-8b3d-8968-0fb7-48a1d34042bf@intel.com>
2020-07-16 4:20 ` Jason Wang [this message]
2020-07-16 6:15 ` Michael S. Tsirkin
2020-07-16 8:06 ` Jason Wang
2020-07-16 6:13 ` Michael S. Tsirkin
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