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Date: Tue, 23 Mar 2010 07:47:18 -0700
From: Badari Pulavarty <pbadari@us.ibm.com>
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Subject: [Qemu-devel] Re: [RFC] vhost-blk implementation
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org

Michael S. Tsirkin wrote:
> On Mon, Mar 22, 2010 at 05:34:04PM -0700, Badari Pulavarty wrote:
>   
>> Write Results:
>> ==============
>>
>> I see degraded IO performance when doing sequential IO write
>> tests with vhost-blk compared to virtio-blk.
>>
>> # time dd of=/dev/vda if=/dev/zero bs=2M oflag=direct
>>
>> I get ~110MB/sec with virtio-blk, but I get only ~60MB/sec with
>> vhost-blk. Wondering why ?
>>     
>
> Try to look and number of interrupts and/or number of exits.
>
> It could also be that you are overrunning some queue.
>   

Yeah.
> I don't see any exit mitigation strategy in your patch:
> when there are already lots of requests in a queue, it's usually
> a good idea to disable notifications and poll the
> queue as requests complete. That could help performance.
>   

Thanks for the suggestions. I will take a closer look.

Thanks,
Badari