On Thu, Nov 13, 2025 at 8:14 AM Jon Kohler <[email protected]> wrote: > > vhost_get_user and vhost_put_user leverage __get_user and __put_user, > respectively, which were both added in 2016 by commit 6b1e6cc7855b > ("vhost: new device IOTLB API").
It has been used even before this commit. > In a heavy UDP transmit workload on a > vhost-net backed tap device, these functions showed up as ~11.6% of > samples in a flamegraph of the underlying vhost worker thread. > > Quoting Linus from [1]: > Anyway, every single __get_user() call I looked at looked like > historical garbage. [...] End result: I get the feeling that we > should just do a global search-and-replace of the __get_user/ > __put_user users, replace them with plain get_user/put_user instead, > and then fix up any fallout (eg the coco code). > > Switch to plain get_user/put_user in vhost, which results in a slight > throughput speedup. get_user now about ~8.4% of samples in flamegraph. > > Basic iperf3 test on a Intel 5416S CPU with Ubuntu 25.10 guest: > TX: taskset -c 2 iperf3 -c <rx_ip> -t 60 -p 5200 -b 0 -u -i 5 > RX: taskset -c 2 iperf3 -s -p 5200 -D > Before: 6.08 Gbits/sec > After: 6.32 Gbits/sec I wonder if we need to test on archs like ARM. Thanks
