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

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Message-ID: <20201209105829.6l6ie7xqp2eycds6@steredhat>
Date:   Wed, 9 Dec 2020 11:58:29 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        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 Mon, Dec 07, 2020 at 12:00:07PM +0800, Jason Wang wrote:
>
>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?
>

No, I didn't try with the limit.
This came from the reviews to Max's patches.

Anyway I can add a module parameter to control that limit, do you think 
is better to set a limit per queue (the parameter per number of queues), 
or just a value for the entire device?

Thanks,
Stefano