Re: Cache Invalidation Solution for Nested IOMMU

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

On Sun, Apr 09, 2023 at 06:08:25PM -0700, Nicolin Chen wrote:
> On Thu, Apr 06, 2023 at 08:40:04AM -0300, Jason Gunthorpe wrote:
> > On Thu, Apr 06, 2023 at 02:23:17PM +0800, Zhangfei Gao wrote:
> > 
> > > We are using ioctl method now.
> > > From the testing, the TLB miss impacts performance a lot, so we use
> > > huge page method.
> > > After using huge page method, guest can achieve comparable performance
> > > with host.
> > 
> > Looks like these tests are not stressing the MM, just measuring pure
> > BW of the DMA, so they don't get into the invalidation regime..
> > 
> > You need to measure a more real application that is actually using the
> > MM (eg alloc/free memory, fork, etc) while it operates and turn on SVA.
> 
> Would an iommu map/unmap benchmark test be useful here?

You can reuse and improve dma_map_benchmark, already upstream. It supports
multi-threads and reports stddev. For some comparisons the report
resolution (.1 us) is insufficient and needs to be increased, but for
comparing guest performance it might be alright.

https://lore.kernel.org/linux-iommu/20201102080646.2180-2-song.bao.hua@hisilicon.com/

Thanks,
Jean