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

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Date:	Mon, 08 Aug 2011 10:16:17 -0700
From:	Badari Pulavarty <pbadari@...ibm.com>
To:	Liu Yuan <namei.unix@...il.com>
CC:	Stefan Hajnoczi <stefanha@...il.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Avi Kivity <avi@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Khoa Huynh <khoa@...ibm.com>
Subject: Re: [RFC PATCH]vhost-blk: In-kernel accelerator for virtio block
 device

On 8/8/2011 12:31 AM, Liu Yuan wrote:
> On 08/08/2011 01:04 PM, Badari Pulavarty wrote:
>> On 8/7/2011 6:35 PM, Liu Yuan wrote:
>>> On 08/06/2011 02:02 AM, Badari Pulavarty wrote:
>>>> On 8/5/2011 4:04 AM, Liu Yuan wrote:
>>>>> On 08/05/2011 05:58 AM, Badari Pulavarty wrote:
>>>>>> Hi Liu Yuan,
>>>>>>
>>>>>> I started testing your patches. I applied your kernel patch to 3.0
>>>>>> and applied QEMU to latest git.
>>>>>>
>>>>>> I passed 6 blockdevices from the host to guest (4 vcpu, 4GB RAM).
>>>>>> I ran simple "dd" read tests from the guest on all block devices
>>>>>> (with various blocksizes, iflag=direct).
>>>>>>
>>>>>> Unfortunately, system doesn't stay up. I immediately get into
>>>>>> panic on the host. I didn't get time to debug the problem. Wondering
>>>>>> if you have seen this issue before and/or you have new patchset
>>>>>> to try ?
>>>>>>
>>>>>> Let me know.
>>>>>>
>>>>>> Thanks,
>>>>>> Badari
>>>>>>
>>>>>
>>>>> Okay, it is actually a bug pointed out by MST on the other thread, 
>>>>> that it needs a mutex for completion thread.
>>>>>
>>>>> Now would you please this attachment?This patch only applies to 
>>>>> kernel part, on top of v1 kernel patch.
>>>>>
>>>>> This patch mainly moves completion thread into vhost thread as a 
>>>>> function. As a result, both requests submitting and completion 
>>>>> signalling is in the same thread.
>>>>>
>>>>> Yuan
>>>>
>>>> Unfortunately, "dd" tests (4 out of 6) in the guest hung. I see 
>>>> following messages
>>>>
>>>> virtio_blk virtio2: requests: id 0 is not a head !
>>>> virtio_blk virtio3: requests: id 1 is not a head !
>>>> virtio_blk virtio5: requests: id 1 is not a head !
>>>> virtio_blk virtio1: requests: id 1 is not a head !
>>>>
>>>> I still see host panics. I will collect the host panic and see if 
>>>> its still same or not.
>>>>
>>>> Thanks,
>>>> Badari
>>>>
>>>>
>>> Would you please show me how to reproduce it step by step? I tried 
>>> dd with two block device attached, but didn't get hung nor panic.
>>>
>>> Yuan
>>
>> I did 6 "dd"s on 6 block devices..
>>
>> dd if=/dev/vdb of=/dev/null bs=1M iflag=direct &
>> dd if=/dev/vdc of=/dev/null bs=1M iflag=direct &
>> dd if=/dev/vdd of=/dev/null bs=1M iflag=direct &
>> dd if=/dev/vde of=/dev/null bs=1M iflag=direct &
>> dd if=/dev/vdf of=/dev/null bs=1M iflag=direct &
>> dd if=/dev/vdg of=/dev/null bs=1M iflag=direct &
>>
>> I can reproduce the problem with in 3 minutes :(
>>
>> Thanks,
>> Badari
>>
>>
> Ah...I made an embarrassing mistake that I tried to 'free()' an 
> kmem_cache object.
>
> Would you please revert the vblk-for-kernel-2 patch and apply the new 
> one attached in this letter?
>
Hmm.. My version of the code seems to have kzalloc() for used_info. I 
don't have a version
that is using kmem_cache_alloc(). Would it be possible for you to send 
out complete patch
(with all the fixes applied) for me to try ? This will avoid all the 
confusion ..

Thanks,
Badari


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