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From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: 谢华伟(此时此刻) <huawei.xhw@alibaba-inc.com>, ferruh.yigit@intel.com
Cc: dev@dpdk.org, anatoly.burakov@intel.com,
	david.marchand@redhat.com, zhihong.wang@intel.com,
	chenbo.xia@intel.com, grive@u256.net
Subject: Re: [dpdk-dev] [PATCH v5 0/3] support both PIO and MMIO BAR for virtio PMD
Date: Thu, 21 Jan 2021 09:47:54 +0100
Message-ID: <5791302d-4e43-9b26-860f-83d066060a02@redhat.com> (raw)
In-Reply-To: <4a2bfa2c-5911-1281-3684-0250665e4901@alibaba-inc.com>



On 1/21/21 5:12 AM, 谢华伟(此时此刻) wrote:
> 
> On 2021/1/13 1:37, Maxime Coquelin wrote:
>>
>> On 10/22/20 5:51 PM, 谢华伟(此时此刻) wrote:
>>> From: "huawei.xhw" <huawei.xhw@alibaba-inc.com>
>>>
>>> Legacy virtio-pci only supports PIO BAR resource. As we need to
>>> create lots of
>>> virtio devices and PIO resource on x86 is very limited, we expose
>>> MMIO BAR.
>>>
>>> Kernel supports both PIO  and MMIO BAR for legacy virtio-pci device.
>>> We handles
>>> different type of BAR in the similar way.
>>>
>>> In previous implementation, with igb_uio we get PIO address from igb_uio
>>> sysfs entry; with uio_pci_generic, we get PIO address from
>>> /proc/ioports.
>>> For PIO/MMIO RW, there is different path for different drivers and arch.
>>> For VFIO, PIO/MMIO RW is through syscall, which has big performance
>>> issue.
>> Regarding the performance issue, do you have some numbers to share?
>> AFAICS, it can only have an impact on performance when interrupt mode is
>> used or queue notification is enabled.
>>
>> Does your HW Virtio implementation requires notification?
> 
> Yes, hardware needs notification to tell which queue has more buffer.
> 
> vhost backend also needs notification when it is not running in polling
> mode.
> 
> It is easy for software backend to sync with frontend whether it needs
> notification through memory but a big burden for hardware.

Yes, I understand, thanks for the clarification.

> Anyway, using vfio ioctl isn't needed at all. virtio PMD is only the
> consumer of pci_vfio_ioport_read.

My understanding is that using VFIO read/write ops is required for IOMMU
enabled case without cap_sys_rawio. And anyway, using inb/outb is just
bypassing VFIO. As I suggest in my other reply, it is better to document
that in the case of devices having PIO BARs, the user should consider
using UIO driver if performance is a concern.

> we could consider if we still need pci_vfio_ioport_read related API in
> future.

I disagree. I think the pci_vfio_ioport_* API is required at least for
the IOMMU enabled case.

Documentation is the way to go in my opinion, we can also add a warning
that performance may be degraded compared to UIO in
pci_vfio_ioport_map() when IOMMU is disabled if you think it may help
the users.

Thanks,
Maxime

> /huawei
>>
>> Is performance the only issue to have your HW working with Virtio PMD,
>> or is this series also fixing some functionnal issues?
>>
>> Best regards,
>> Maxime
>>
> 


  reply	other threads:[~2021-01-21  8:48 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-30 14:59 [dpdk-dev] [PATCH v2] pci: support both PIO and MMIO BAR for legacy virtio on x86 谢华伟(此时此刻)
2020-10-01 10:22 ` Burakov, Anatoly
2020-10-02  5:44   ` 谢华伟(此时此刻)
2020-10-09  8:36 ` [dpdk-dev] [PATCH v3] " 谢华伟(此时此刻)
2020-10-13  8:41 ` [dpdk-dev] [PATCH v4] support both PIO and MMIO bar for virtio pci device 谢华伟(此时此刻)
2020-10-13  8:41   ` [dpdk-dev] [PATCH v4] pci: support both PIO and MMIO BAR for legacy virtio on x86 谢华伟(此时此刻)
2020-10-13 12:34     ` 谢华伟(此时此刻)
2020-10-21  8:46     ` 谢华伟(此时此刻)
2020-10-21 11:49     ` Ferruh Yigit
2020-10-21 12:32       ` 谢华伟(此时此刻)
2020-10-21 17:24         ` Ferruh Yigit
2020-10-22  9:15           ` 谢华伟(此时此刻)
2020-10-22  9:44             ` Ferruh Yigit
2020-10-22  9:57               ` 谢华伟(此时此刻)
2020-10-22 15:51 ` [dpdk-dev] [PATCH v5 0/3] support both PIO and MMIO BAR for virtio PMD 谢华伟(此时此刻)
2020-10-22 15:51   ` [dpdk-dev] [PATCH v5 1/3] PCI: use PCI standard sysfs entry to get PIO address 谢华伟(此时此刻)
2021-01-12  8:07     ` Maxime Coquelin
2021-01-14 18:23       ` 谢华伟(此时此刻)
2021-01-24 15:10         ` Xueming(Steven) Li
2020-10-22 15:51   ` [dpdk-dev] [PATCH v5 2/3] PCI: support MMIO in rte_pci_ioport_map/unap/read/write 谢华伟(此时此刻)
2021-01-12  8:23     ` Maxime Coquelin
2021-01-21  6:30       ` 谢华伟(此时此刻)
2021-01-24 15:22     ` Xueming(Steven) Li
2021-01-25  3:08       ` 谢华伟(此时此刻)
2021-01-27 10:40     ` Ferruh Yigit
2021-01-27 15:34       ` 谢华伟(此时此刻)
2021-01-27 16:45         ` Ferruh Yigit
2020-10-22 15:51   ` [dpdk-dev] [PATCH v5 3/3] PCI: don't use vfio ioctl call to access PIO resource 谢华伟(此时此刻)
2021-01-12  9:37     ` Maxime Coquelin
2021-01-12 16:58       ` Maxime Coquelin
2021-01-20 14:54         ` 谢华伟(此时此刻)
2021-01-21  8:29           ` Maxime Coquelin
2021-01-21 14:57             ` 谢华伟(此时此刻)
2021-01-21 15:00               ` 谢华伟(此时此刻)
2021-01-21 15:38               ` Maxime Coquelin
2021-01-22  7:25                 ` 谢华伟(此时此刻)
2021-01-26 10:44                   ` Maxime Coquelin
2021-01-27 10:32                     ` Ferruh Yigit
2021-01-27 12:17                       ` Maxime Coquelin
2021-01-27 14:43                       ` 谢华伟(此时此刻)
2021-01-27 16:45                         ` Ferruh Yigit
2021-01-28 13:43                           ` 谢华伟(此时此刻)
2021-01-26 12:30                   ` 谢华伟(此时此刻)
2021-01-26 12:35                     ` Maxime Coquelin
2021-01-26 14:24                       ` 谢华伟(此时此刻)
2020-10-27  8:50   ` [dpdk-dev] [PATCH v5 0/3] support both PIO and MMIO BAR for virtio PMD 谢华伟(此时此刻)
2020-10-28  3:48     ` 谢华伟(此时此刻)
2020-11-02 11:56   ` 谢华伟(此时此刻)
2020-11-10 12:35   ` 谢华伟(此时此刻)
2020-11-10 12:42     ` David Marchand
2020-11-12 13:35       ` 谢华伟(此时此刻)
2020-12-14 14:24       ` 谢华伟(此时此刻)
2020-12-16  7:54         ` Maxime Coquelin
2021-01-12 17:37   ` Maxime Coquelin
2021-01-14 18:19     ` 谢华伟(此时此刻)
2021-01-21  4:12     ` 谢华伟(此时此刻)
2021-01-21  8:47       ` Maxime Coquelin [this message]
2021-01-21 13:51         ` 谢华伟(此时此刻)

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