Re: [PATCH V2 1/2] Swiotlb: Add swiotlb_alloc_from_low_pages switch

[Tianyu Lan]

On 2/22/2022 4:05 PM, Christoph Hellwig wrote:
> On Mon, Feb 21, 2022 at 11:14:58PM +0800, Tianyu Lan wrote:
> > Sorry. The boot failure is not related with these patches and the issue
> > has been fixed in the latest upstream code.
> >
> > There is a performance bottleneck due to io tlb mem's spin lock during
> > performance test. All devices'io queues uses same io tlb mem entry
> > and the spin lock of io tlb mem introduce overheads. There is a fix patch
> > from Andi Kleen in the github. Could you have a look?
> >
> > https://github.com/intel/tdx/commit/4529b5784c141782c72ec9bd9a92df2b68cb7d45
>
> Please post these things to the list.
>
> But I suspect the right answer for the "secure" hypervisor case is to
> use the per-device swiotlb regions that we've recently added.

Thanks for your comment. That means we need to expose an 
swiotlb_device_init() interface to allocate bounce buffer and initialize
io tlb mem entry. DMA API Current  rmem_swiotlb_device_init() only works
for platform with device tree. The new API should be called in the bus
driver or new DMA API. Could you check whether this is a right way 
before we start the work.

Thanks.