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Donenfeld" Cc: Andrew Morton , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Michael Ellerman , Nicholas Piggin , Naveen N Rao , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Shuah Khan , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kselftest@vger.kernel.org, llvm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, Adhemerval Zanella Date: Fri, 06 Sep 2024 01:01:13 +0800 In-Reply-To: <85c02620-e8b2-4c97-9905-685a9a4e556d@csgroup.eu> References: <1f49c2ce009f8b007ab0676fb41187b2d54f28b2.1725304404.git.christophe.leroy@csgroup.eu> <85c02620-e8b2-4c97-9905-685a9a4e556d@csgroup.eu> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.3 MIME-Version: 1.0 X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: E2C20100013 X-Stat-Signature: k6n6pai5sgzeurmd8c5ys3b14zhcw5tf X-HE-Tag: 1725555694-963296 X-HE-Meta: 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 dYXpbAp1 xRyZx/4xZZDPBi7KNImsaeTQuULoz2F1HCOzgvuJoUzaU9c1+gFNwCM4jkQIR7z3RQkZaS9p0jF75x7kGz/hVjHxf9TJFdTQMAiqsEfreCL7GeKuUDrylxNKVrZ6q+Qdd5VqapTF0GZJC3uHTYihY1imU11qXwz9jpJbFQ3WCLwNbw/PVkVPlwZg+e7xKLvdygAmkYQauJJ/1OsTiCgzaYFt/PW4l1CMl7I5uyV/pnTZqhX95qF9hGx4ul/m2YeR5dHnRMzOMc7nw2cey36EChpiw9QY31uYI0EjXxu7MG0XeR6wzuH0rSBtafIoXwSikPH5ay872hWGHzp3iCnp28owyGQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 2024-09-05 at 18:55 +0200, Christophe Leroy wrote: > > Normal single thread > > =C2=A0=C2=A0=C2=A0=C2=A0 vdso: 25000000 times in 12.494133131 seconds > > =C2=A0=C2=A0=C2=A0=C2=A0 libc: 25000000 times in 69.594625188 seconds > > syscall: 25000000 times in 67.349243972 seconds > > Time namespace single thread > > =C2=A0=C2=A0=C2=A0=C2=A0 vdso: 25000000 times in 71.673057436 seconds > > =C2=A0=C2=A0=C2=A0=C2=A0 libc: 25000000 times in 71.712774121 seconds > > syscall: 25000000 times in 66.902318080 seconds > >=20 > > I'm seeing this on ppc, ppc64, and ppc64le. >=20 > 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. --=20 Xi Ruoyao School of Aerospace Science and Technology, Xidian University