From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: Bruce Richardson <bruce.richardson@intel.com>
Cc: "Hu, Jiayu" <jiayu.hu@intel.com>,
"Wang, YuanX" <yuanx.wang@intel.com>,
"Xia, Chenbo" <chenbo.xia@intel.com>,
"dev@dpdk.org" <dev@dpdk.org>,
"Jiang, Cheng1" <cheng1.jiang@intel.com>,
"Ma, WenwuX" <wenwux.ma@intel.com>,
"He, Xingguang" <xingguang.he@intel.com>,
Thomas Monjalon <thomas@monjalon.net>,
Ilya Maximets <imaximet@redhat.com>,
David Marchand <david.marchand@redhat.com>
Subject: Re: [PATCH v5] net/vhost: support asynchronous data path
Date: Tue, 25 Oct 2022 18:04:48 +0200 [thread overview]
Message-ID: <e83bc805-1665-4879-76c9-bb24e70f81ba@redhat.com> (raw)
In-Reply-To: <Y1gEXToayG69VERE@bricha3-MOBL.ger.corp.intel.com>
On 10/25/22 17:44, Bruce Richardson wrote:
> On Tue, Oct 25, 2022 at 05:33:31PM +0200, Maxime Coquelin wrote:
>>
>>
>> On 10/25/22 11:15, Hu, Jiayu wrote:
>
>>>> I think that for Vhost PMD, the Virtio completions should either be
>>>> performed by DMA engine or by a dedicated thread.
>>>
>>> We cannot depend on DMA engine to do completion, as there is no
>>> ordering guarantee on the HW. For example, given the DMA engine
>>> issues two updates on the used ring's index, it is possible that the second
>>> write completes before the first one.
>>
>> I'm not sure for Intel hardware, but other vendors may offer ordering
>> guarantees, it should be exposed as a capability of the DMA device. If
>> the DMA device offers this capability, it could be used for Vhost.
>>
>
> While I haven't been following this discussion, this particular comment
> caught my eye.
>
> For jobs submitted via a single dmadev device, the "FENCE" flag is provided
> as part of the dmadev API[1]. Obviously, if the writes come from different
> dmadevs, then things are rather more complicated.
Thanks for the clarification Bruce.
In the Vhost PMD case, there is a 1:1 mapping between the virtqueue and
the DMA channel, so we should be fine.
Regards,
Maxime
> /Bruce
>
>
> [1] https://doc.dpdk.org/api/rte__dmadev_8h.html#a3375e7b956b305505073c4ff035afe2f
>
next prev parent reply other threads:[~2022-10-25 16:04 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-14 15:06 [PATCH] " Jiayu Hu
2022-08-18 2:05 ` [PATCH v2] " Jiayu Hu
2022-08-23 16:35 ` [PATCH v3] " Yuan Wang
2022-09-26 6:55 ` Xia, Chenbo
2022-09-27 7:34 ` Wang, YuanX
2022-09-28 8:13 ` Wang, YuanX
2022-10-10 5:17 ` Hu, Jiayu
2022-10-18 11:59 ` Xia, Chenbo
2022-09-29 19:47 ` [PATCH v4] " Yuan Wang
2022-10-19 14:10 ` Xia, Chenbo
2022-10-20 14:00 ` Wang, YuanX
2022-10-24 15:14 ` [PATCH v5] " Yuan Wang
2022-10-24 9:02 ` Xia, Chenbo
2022-10-24 9:25 ` Wang, YuanX
2022-10-24 9:08 ` Maxime Coquelin
2022-10-25 2:14 ` Hu, Jiayu
2022-10-25 7:52 ` Maxime Coquelin
2022-10-25 9:15 ` Hu, Jiayu
2022-10-25 15:33 ` Maxime Coquelin
2022-10-25 15:44 ` Bruce Richardson
2022-10-25 16:04 ` Maxime Coquelin [this message]
2022-10-26 2:48 ` Hu, Jiayu
2022-10-26 5:00 ` Maxime Coquelin
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