On Thu, 2024-09-05 at 18:55 +0200, Christophe Leroy wrote: > > Normal single thread > > vdso: 25000000 times in 12.494133131 seconds > > libc: 25000000 times in 69.594625188 seconds > > syscall: 25000000 times in 67.349243972 seconds > > Time namespace single thread > > vdso: 25000000 times in 71.673057436 seconds > > libc: 25000000 times in 71.712774121 seconds > > syscall: 25000000 times in 66.902318080 seconds > > > > I'm seeing this on ppc, ppc64, and ppc64le. > > What is the command to use to test with time namespace ? Assuming user namespace and time namespace are available: $ unshare -r -T --boottime $((365*24*3600)) It'll start a new shell where you are pretended to be the root (i.e. the root in the separated user namespace). Then: # uptime 00:57:17 up 365 days, 57 min, 2 users, load average: 0.19, 0.30, 0.32 So in the separated time namespace the system is pretended to have been booted for 1 year. Now: # /path/to/linux.git/tools/testing/selftests/vDSO/vdso_test_getrandom bench_single vdso: 25000000 times in 0.419125373 seconds libc: 25000000 times in 5.985498234 seconds syscall: 25000000 times in 5.993506773 seconds This is on x86_64, indicating vDSO getrandom is fine for x86_64 in a separated time namespace. If user namespace isn't available (disabled building the kernel or disabled by the security policy of some distros) use $ sudo unshare -T --boottime $((365*24*3600)) to create the time namespace instead. But note that with this approach you'll be operating as the real root user and be careful not to break things. -- Xi Ruoyao <xry111@xxxxxxxxxxx> School of Aerospace Science and Technology, Xidian University
