linux-kernel - Re: [PATCH RFC 00/12] vdpa: generalize vdpa simulator and add block device

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Message-ID: <20201116085311.erzo2z322qesw5in@steredhat>
Date:   Mon, 16 Nov 2020 09:53:11 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Laurent Vivier <lvivier@...hat.com>,
        linux-kernel@...r.kernel.org, Eli Cohen <elic@...dia.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Max Gurtovoy <mgurtovoy@...dia.com>
Subject: Re: [PATCH RFC 00/12] vdpa: generalize vdpa simulator and add block
 device

On Mon, Nov 16, 2020 at 11:37:48AM +0800, Jason Wang wrote:
>
>On 2020/11/13 下午9:47, Stefano Garzarella wrote:
>>Thanks to Max that started this work!
>>I took his patches, and extended the block simulator a bit.
>>
>>This series moves the network device simulator in a new module
>>(vdpa_sim_net) and leaves the generic functions in the vdpa_sim core
>>module, allowing the possibility to add new vDPA device simulators.
>>Then we added a new vdpa_sim_blk module to simulate a block device.
>>
>>I'm not sure about patch 11 ("vringh: allow vringh_iov_xfer() to skip
>>bytes when ptr is NULL"), maybe we can add a new functions instead of
>>modify vringh_iov_xfer().
>>
>>As Max reported, I'm also seeing errors with vdpa_sim_blk related to
>>iotlb and vringh when there is high load, these are some of the error
>>messages I can see randomly:
>>
>>   vringh: Failed to access avail idx at 00000000e8deb2cc
>>   vringh: Failed to read head: idx 6289 address 00000000e1ad1d50
>>   vringh: Failed to get flags at 000000006635d7a3
>>
>>   virtio_vdpa vdpa0: vringh_iov_push_iotlb() error: -14 offset: 0x2840000 len: 0x20000
>>   virtio_vdpa vdpa0: vringh_iov_pull_iotlb() error: -14 offset: 0x58ee000 len: 0x3000
>>
>>These errors should all be related to the fact that iotlb_translate()
>>fails with -EINVAL, so it seems that we miss some mapping.
>
>
>Is this only reproducible when there's multiple co-current accessing 
>of IOTLB? If yes, it's probably a hint that some kind of 
>synchronization is still missed somewhere.

Yeah, maybe this is the case where virtio_ring and vringh use IOTLB 
concorrentetively.

>
>It might be useful to log the dma_map/unmp in both virtio_ring and 
>vringh to see who is missing the map.

I'll try.

Thanks for the hints,
Stefano