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Re: [Qemu-devel] [PATCH v7 RFC] block/vxhs: Initial commit to add Verita


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v7 RFC] block/vxhs: Initial commit to add Veritas HyperScale VxHS block device support
Date: Wed, 9 Nov 2016 13:47:22 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0


On 08/11/2016 16:39, Stefan Hajnoczi wrote:
> The current status is:
> 
> 1. virtio-blk and virtio-scsi support multiple queues but these queues
>    are processed from a single thread today.
> 
> 2. MemoryRegions can be marked with !global_locking so its handler
>    functions are dispatched without taking the QEMU global mutex.  This
>    allows device emulation to run in multiple threads.

Alternatively, virtio-blk and virtio-scsi can already use ioeventfd and
"-object iothread,id=FOO -device virtio-blk-pci,iothread=FOO" to let
device emulation run in a separate thread that doesn't take the QEMU
global mutex.

> 3. Paolo Bonzini (CCed) is currently working on make the block layer
>    (BlockDriverState and co) support access from multiple threads and
>    multiqueue.  This is work in progress.
> 
> If you are interested in this work keep an eye out for patch series from
> Paolo Bonzini and Fam Zheng.

The first part (drop RFifoLock) was committed for 2.8.  It's a
relatively long road, but these are the currently ready parts of the work:

- take AioContext acquire/release in small critical sections
- push AioContext down to individual callbacks
- make BlockDriverState thread-safe

The latter needs rebasing after the last changes to dirty bitmaps, but I
think these patches should be ready for 2.9.

These are the planned bits:

- replace AioContext with fine-grained mutex in bdrv_aio_*
- protect everything with CoMutex in bdrv_co_*
- remove aio_context_acquire/release

For now I was not planning to make network backends support multiqueue,
only files.

Paolo



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