On Fri, Nov 14, 2025 at 10:53 PM Jon Kohler <[email protected]> wrote: > > > > > On Nov 12, 2025, at 8:09 PM, Jason Wang <[email protected]> wrote: > > > > !-------------------------------------------------------------------| > > CAUTION: External Email > > > > |-------------------------------------------------------------------! > > > > 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. > > Ah, thanks for the pointer. I’d have to go dig to find its genesis, but > its more to say, this existed prior to the LFENCE 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. > > Are you thinking from a performance perspective? Or a correctness one?
Performance, I think the patch is correct. Thanks
