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

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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. :(

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