Re: [RFC PATCH]vhost-blk: In-kernel accelerator for virtio block device

[Liu Yuan <namei.unix@gmail.com>]

On 08/11/2011 11:01 AM, Liu Yuan wrote:
>
>> It looks like the patch wouldn't work for testing multiple devices.
>>
>> vhost_blk_open() does
>> +       used_info_cachep = KMEM_CACHE(used_info, SLAB_HWCACHE_ALIGN |
>> SLAB_PANIC);
>>
>
> This is weird. how do you open multiple device?I just opened the 
> device with following command:
>
> -drive file=/dev/sda6,if=virtio,cache=none,aio=native -drive 
> file=~/data0.img,if=virtio,cache=none,aio=native -drive 
> file=~/data1.img,if=virtio,cache=none,aio=native
>
> And I didn't meet any problem.
>
> this would tell qemu to open three devices, and pass three FDs to 
> three instances of vhost_blk module.
> So KMEM_CACHE() is okay in vhost_blk_open().
>

Oh, you are right. KMEM_CACHE() is in the wrong place. it is three 
instances vhost worker threads created. Hmmm, but I didn't meet any 
problem when opening it and running it. So strange. I'll go to figure it 
out.

>> When opening second device, we get panic since used_info_cachep is
>> already created. Just to make progress I moved this call to
>> vhost_blk_init().
>>
>> I don't see any host panics now. With single block device (dd),
>> it seems to work fine. But when I start testing multiple block
>> devices I quickly run into hangs in the guest. I see following
>> messages in the guest from virtio_ring.c:
>>
>> virtio_blk virtio2: requests: id 0 is not a head !
>> virtio_blk virtio1: requests: id 0 is not a head !
>> virtio_blk virtio4: requests: id 1 is not a head !
>> virtio_blk virtio3: requests: id 39 is not a head !
>>
>> Thanks,
>> Badari
>>
>>
>
> vq->data[] is initialized by guest virtio-blk driver and vhost_blk is 
> unware of it. it looks like used ID passed
> over by vhost_blk to guest virtio_blk is wrong, but, it should not 
> happen. :|
>
> And I can't reproduce this on my laptop. :(
>
>> -- 
>> To unsubscribe from this list: send the line "unsubscribe kvm" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>