On Thu, 19 Apr 2018 01:37:41 +0000 "Wuzongyong (Euler Dept)" <cordius...@huawei.com> wrote:
> > > Hi, > > > > > > The qemu process will stuck when hot-add large size memory to the > > > virtual machine with a device passtrhough. > > > We found it is too slow to pin and map pages in vfio_dma_do_map. > > > Is there any method to improve this process? > > > > At what size do you start to see problems? The time to map a section of > > memory should be directly proportional to the size. As the size is > > increased, it will take longer, but I don't know why you'd reach a point > > of not making forward progress. Is it actually stuck or is it just taking > > longer than you want? Using hugepages can certainly help, we still need > > to pin each PAGE_SIZE page within the hugepage, but we'll have larger > > contiguous regions and therefore call iommu_map() less frequently. Please > > share more data. Thanks, > > > > Alex > It just take longer time, instead of actually stuck. > We found that the problem exist when we hot-added 16G memory. And it will > consume > tens of minutes when we hot-added 1T memory. Is the stall adding 1TB roughly 64 times the stall adding 16GB or do we have some inflection in the size vs time curve? There is a cost to pinning an mapping through the IOMMU, perhaps we can improve that, but I don't see how we can eliminate it or how it wouldn't be at least linear compared to the size of memory added without moving to a page request model, which hardly any hardware currently supports. A workaround might be to incrementally add memory in smaller chunks which generate a less noticeable stall. Thanks, Alex _______________________________________________ vfio-users mailing list vfio-users@redhat.com https://www.redhat.com/mailman/listinfo/vfio-users
