Messages in this thread | | | Subject | Re: [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap() | From | Jason Wang <> | Date | Tue, 12 Mar 2019 10:59:09 +0800 |
| |
On 2019/3/12 上午2:14, David Miller wrote: > From: "Michael S. Tsirkin" <mst@redhat.com> > Date: Mon, 11 Mar 2019 09:59:28 -0400 > >> On Mon, Mar 11, 2019 at 03:13:17PM +0800, Jason Wang wrote: >>> On 2019/3/8 下午10:12, Christoph Hellwig wrote: >>>> On Wed, Mar 06, 2019 at 02:18:07AM -0500, Jason Wang wrote: >>>>> 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. This is done through setup kernel address through vmap() and >>>>> resigter MMU notifier for invalidation. >>>>> >>>>> Test shows about 24% improvement on TX PPS. TCP_STREAM doesn't see >>>>> obvious improvement. >>>> How is this going to work for CPUs with virtually tagged caches? >>> >>> Anything different that you worry? >> If caches have virtual tags then kernel and userspace view of memory >> might not be automatically in sync if they access memory >> through different virtual addresses. You need to do things like >> flush_cache_page, probably multiple times. > "flush_dcache_page()"
I get this. Then I think the current set_bit_to_user() is suspicious, we probably miss a flush_dcache_page() there:
static int set_bit_to_user(int nr, void __user *addr) { unsigned long log = (unsigned long)addr; struct page *page; void *base; int bit = nr + (log % PAGE_SIZE) * 8; int r;
r = get_user_pages_fast(log, 1, 1, &page); if (r < 0) return r; BUG_ON(r != 1); base = kmap_atomic(page); set_bit(bit, base); kunmap_atomic(base); set_page_dirty_lock(page); put_page(page); return 0; }
Thanks
| |