linux-kernel - Re: [RFC PATCH 0/7] Untrusted device support for virtio

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Date:   Sun, 25 Apr 2021 09:43:17 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, xieyongji@...edance.com,
        stefanha@...hat.com, file@...t.tu-berlin.de, ashish.kalra@....com,
        martin.radev@...ec.fraunhofer.de, konrad.wilk@...cle.com,
        kvm@...r.kernel.org
Subject: Re: [RFC PATCH 0/7] Untrusted device support for virtio


在 2021/4/24 上午4:14, Michael S. Tsirkin 写道:
> On Thu, Apr 22, 2021 at 04:19:16PM +0800, Jason Wang wrote:
>> 在 2021/4/22 下午2:31, Christoph Hellwig 写道:
>>> On Wed, Apr 21, 2021 at 11:21:10AM +0800, Jason Wang wrote:
>>>> The behaivor for non DMA API is kept for minimizing the performance
>>>> impact.
>>> NAK.  Everyone should be using the DMA API in a modern world.  So
>>> treating the DMA API path worse than the broken legacy path does not
>>> make any sense whatsoever.
>>
>> I think the goal is not treat DMA API path worse than legacy. The issue is
>> that the management layer should guarantee that ACCESS_PLATFORM is set so
>> DMA API is guaranteed to be used by the driver. So I'm not sure how much
>> value we can gain from trying to 'fix' the legacy path. But I can change the
>> behavior of legacy path to match DMA API path.
>>
>> Thanks
> I think before we maintain different paths with/without ACCESS_PLATFORM
> it's worth checking whether it's even a net gain. Avoiding sharing
> by storing data in private memory can actually turn out to be
> a net gain even without DMA API.


I agree.


>
> It is worth checking what is the performance effect of this patch.


So I've posted v2, where private memory is used in no DMA API path (as 
what has been done in packed).

Pktgen and netperf doens't see obvious difference.

Thanks


>
>