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Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool


From: Anthony Liguori
Subject: Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool
Date: Fri, 12 Dec 2008 14:17:59 -0600
User-agent: Thunderbird 2.0.0.17 (X11/20080925)

Gerd Hoffmann wrote:
Andrea Arcangeli wrote:
On Fri, Dec 12, 2008 at 12:17:58PM -0600, Anthony Liguori wrote:
You assume that anything using bdrv_aio_readv/writev will be going through a DMA API. This isn't a safe assumption.
Well it's obviously a safe assumption right now... ;)

Well, the xen block backend in my xen patch queue calls bdrv_* directly
right now.  Dunno whenever it is possible/useful to fit the grant table
stuff into the upcoming dma api somehow.

I don't know about grant table references b/c that's really foreign memory. But this is a good argument against the DMA as it stands, b/c you may be handing foreign memory to bdrv_aio_readv/writev.

A big reason for the map/unmap lock/unlock abstraction though would be the qemu-dm map cache. I think you could use it to pretty reasonably integrate the map cache which I know I've previously could never be done :-)

Regards,

Anthony Liguori

cheers,
  Gerd

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