linux-kernel - Re: [PATCH v3 05/19] vdpa_sim: remove the limit of IOTLB entries

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Date:   Mon, 7 Dec 2020 12:00:07 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>,
        virtualization@...ts.linux-foundation.org
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>, Oren Duer <oren@...dia.com>,
        Laurent Vivier <lvivier@...hat.com>,
        linux-kernel@...r.kernel.org, Max Gurtovoy <mgurtovoy@...dia.com>,
        Shahaf Shuler <shahafs@...dia.com>, Eli Cohen <elic@...dia.com>
Subject: Re: [PATCH v3 05/19] vdpa_sim: remove the limit of IOTLB entries


On 2020/12/4 上午1:04, Stefano Garzarella wrote:
> The simulated devices can support multiple queues, so this limit
> should be defined according to the number of queues supported by
> the device.
>
> Since we are in a simulator, let's simply remove that limit.
>
> Suggested-by: Jason Wang <jasowang@...hat.com>
> Acked-by: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>


Rethink about this, since simulator can be used by VM, so the allocation 
is actually guest trigger-able when vIOMMU is enabled.

This means we need a limit somehow, (e.g I remember swiotlb is about 
64MB by default). Or having a module parameter for this.

Btw, have you met any issue when using 2048, I guess it can happen when 
we run several processes in parallel?


> ---
> v3:
> - used VHOST_IOTLB_UNLIMITED macro [Jason]
> v2:
> - added VDPASIM_IOTLB_LIMIT macro [Jason]
> ---
>   drivers/vdpa/vdpa_sim/vdpa_sim.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index 295a770caac0..688aceaa6543 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -368,7 +368,7 @@ static struct vdpasim *vdpasim_create(void)
>   	if (!vdpasim->vqs)
>   		goto err_iommu;
>   
> -	vdpasim->iommu = vhost_iotlb_alloc(2048, 0);
> +	vdpasim->iommu = vhost_iotlb_alloc(VHOST_IOTLB_UNLIMITED, 0);
>   	if (!vdpasim->iommu)
>   		goto err_iommu;
>