Messages in this thread | | | Subject | Re: [PATCH net-next V4 0/5] vhost: accelerate metadata access through vmap() | From | Jason Wang <> | Date | Tue, 29 Jan 2019 10:34:46 +0800 |
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On 2019/1/27 上午8:31, Michael S. Tsirkin wrote: > On Sat, Jan 26, 2019 at 02:37:08PM -0800, David Miller wrote: >> From: Jason Wang <jasowang@redhat.com> >> Date: Wed, 23 Jan 2019 17:55:52 +0800 >> >>> This series tries to access virtqueue metadata through kernel virtual >>> address instead of copy_user() friends since they had too much >>> overheads like checks, spec barriers or even hardware feature >>> toggling. >>> >>> Test shows about 24% improvement on TX PPS. It should benefit other >>> cases as well. >> I've read over the discussion of patch #5 a few times. >> >> And it seems to me that, at a minimum, a few things still need to >> be resolved: >> >> 1) More perf data added to commit message.
Ok.
>> >> 2) Whether invalidate_range_start() and invalidate_range_end() must >> be paired.
The reason that vhost doesn't need an invalidate_range_end() is because we have a fallback to copy_to_user() friends. So there's no requirement to setup the mapping in range_end() or lock the vq between range_start() and range_end(). We try to delay the setup of vmap until it will be really used in vhost_meta_prefetch() and we hold mmap_sem when trying to setup vmap, this will guarantee there's no intermediate state at this time.
> > Add dirty tracking.
I think this could be solved by introducing e.g vhost_meta_prefetch_done() at the end of handle_tx()/handle_rx() and call set_page_dirty() for used pages instead of the tricks of classifying VMA. (As I saw hugetlbfs has its own set dirty method).
Thanks
> >> Etc. So I am marking this series "Changes Requested".
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