Re: [PATCH v6 0/5] optimize the downtime for vfio migration

[Alex Williamson]

On Sat, 26 Mar 2022 14:02:21 +0800
"Longpeng(Mike)" <longpeng2@huawei.com> wrote:

> From: Longpeng <longpeng2@huawei.com>
> 
> Hi guys,
>  
> In vfio migration resume phase, the cost would increase if the
> vfio device has more unmasked vectors. We try to optimize it in
> this series.
>  
> You can see the commit message in PATCH 6 for details.
>  
> Patch 1-3 are simple cleanups and fixup.
> Patch 4 are the preparations for the optimization.
> Patch 5 optimizes the vfio msix setup path.
> 
> v5: https://lore.kernel.org/all/20211103081657.1945-1-longpeng2@huawei.com/T/
> 
> Change v5->v6:
>  - remove the Patch 4("kvm: irqchip: extract 
> kvm_irqchip_add_deferred_msi_route")
>     of v5, and use KVMRouteChange API instead. [Paolo, Longpeng]
> 
> Changes v4->v5:
>  - setup the notifier and irqfd in the same function to makes
>    the code neater.    [Alex]
> 
> Changes v3->v4:
>  - fix several typos and grammatical errors [Alex]
>  - remove the patches that fix and clean the MSIX common part
>    from this series [Alex]
>  - Patch 6:
>     - use vector->use directly and fill it with -1 on error
>       paths [Alex]
>     - add comment before enable deferring to commit [Alex]
>     - move the code that do_use/release on vector 0 into an
>       "else" branch [Alex]
>     - introduce vfio_prepare_kvm_msi_virq_batch() that enables
>       the 'defer_kvm_irq_routing' flag [Alex]
>     - introduce vfio_commit_kvm_msi_virq_batch() that clears the
>       'defer_kvm_irq_routing' flag and does further work [Alex]
> 
> Changes v2->v3:
>  - fix two errors [Longpeng]
> 
> Changes v1->v2:
>  - fix several typos and grammatical errors [Alex, Philippe]
>  - split fixups and cleanups into separate patches  [Alex, Philippe]
>  - introduce kvm_irqchip_add_deferred_msi_route to
>    minimize code changes    [Alex]
>  - enable the optimization in msi setup path    [Alex]
> 
> Longpeng (Mike) (5):
>   vfio: simplify the conditional statements in vfio_msi_enable
>   vfio: move re-enabling INTX out of the common helper
>   vfio: simplify the failure path in vfio_msi_enable
>   Revert "vfio: Avoid disabling and enabling vectors repeatedly in VFIO
>     migration"
>   vfio: defer to commit kvm irq routing when enable msi/msix
> 
>  hw/vfio/pci.c | 183 +++++++++++++++++++++++++++++++-------------------
>  hw/vfio/pci.h |   2 +
>  2 files changed, 115 insertions(+), 70 deletions(-)
> 

Nice to see you found a solution with Paolo's suggestion for
begin/commit batching.  Looks ok to me; I'll queue this for after the
v7.0 QEMU release and look for further reviews and comments in the
interim.  Thanks,

Alex