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Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty pa
From: |
Konrad Rzeszutek Wilk |
Subject: |
Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking |
Date: |
Mon, 4 Jan 2016 15:41:04 -0500 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Sun, Dec 13, 2015 at 01:28:09PM -0800, Alexander Duyck wrote:
> This patch set is meant to be the guest side code for a proof of concept
> involving leaving pass-through devices in the guest during the warm-up
> phase of guest live migration. In order to accomplish this I have added a
What does that mean? 'warm-up-phase'?
> new function called dma_mark_dirty that will mark the pages associated with
> the DMA transaction as dirty in the case of either an unmap or a
> sync_.*_for_cpu where the DMA direction is either DMA_FROM_DEVICE or
> DMA_BIDIRECTIONAL. The pass-through device must still be removed before
> the stop-and-copy phase, however allowing the device to be present should
> significantly improve the performance of the guest during the warm-up
> period.
.. if the warm-up phase is short I presume? If the warm-up phase takes
a long time (busy guest that is of 1TB size) it wouldn't help much as the
tracking of these DMA's may be quite long?
>
> This current implementation is very preliminary and there are number of
> items still missing. Specifically in order to make this a more complete
> solution we need to support:
> 1. Notifying hypervisor that drivers are dirtying DMA pages received
.. And somehow giving the hypervisor the GPFN so it can retain the PFN in
the VT-d as long as possible.
> 2. Bypassing page dirtying when it is not needed.
How would this work with with device doing DMA operations _after_ the migration?
That is the driver submits and DMA READ.. migrates away, device is unplugged,
VT-d context is torn down - device does the DMA READ gets an VT-d error...
and what then? How should the device on the other host replay the DMA READ?
>
> The two mechanisms referenced above would likely require coordination with
> QEMU and as such are open to discussion. I haven't attempted to address
> them as I am not sure there is a consensus as of yet. My personal
> preference would be to add a vendor-specific configuration block to the
> emulated pci-bridge interfaces created by QEMU that would allow us to
> essentially extend shpc to support guest live migration with pass-through
> devices.
shpc?
>
> The functionality in this patch set is currently disabled by default. To
> enable it you can select "SWIOTLB page dirtying" from the "Processor type
> and features" menu.
>
> ---
>
> Alexander Duyck (3):
> swiotlb: Fold static unmap and sync calls into calling functions
> xen/swiotlb: Fold static unmap and sync calls into calling functions
> x86: Create dma_mark_dirty to dirty pages used for DMA by VM guest
>
>
> arch/arm/include/asm/dma-mapping.h | 3 +
> arch/arm64/include/asm/dma-mapping.h | 5 +-
> arch/ia64/include/asm/dma.h | 1
> arch/mips/include/asm/dma-mapping.h | 1
> arch/powerpc/include/asm/swiotlb.h | 1
> arch/tile/include/asm/dma-mapping.h | 1
> arch/unicore32/include/asm/dma-mapping.h | 1
> arch/x86/Kconfig | 11 ++++
> arch/x86/include/asm/swiotlb.h | 26 ++++++++
> drivers/xen/swiotlb-xen.c | 92
> +++++++++++++-----------------
> lib/swiotlb.c | 83 ++++++++++++---------------
> 11 files changed, 123 insertions(+), 102 deletions(-)
>
> --
- Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking,
Konrad Rzeszutek Wilk <=
- Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking, Alexander Duyck, 2016/01/04
- Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking, Michael S. Tsirkin, 2016/01/05
- Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking, Dr. David Alan Gilbert, 2016/01/05
- Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking, Michael S. Tsirkin, 2016/01/05
- Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking, Dr. David Alan Gilbert, 2016/01/05
- Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking, Michael S. Tsirkin, 2016/01/05
- Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking, Dr. David Alan Gilbert, 2016/01/05
- Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking, Michael S. Tsirkin, 2016/01/05
- Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking, Michael S. Tsirkin, 2016/01/05
- Re: [Qemu-devel] [RFC PATCH 0/3] x86: Add support for guest DMA dirty page tracking, Michael S. Tsirkin, 2016/01/05