On Mon, Oct 26, 2020 at 10:43:03PM +0100, Marek Szyprowski wrote: > Hi Krzysztof, > > On 22.03.2019 14:10, Krzysztof Kozlowski wrote: > > On Fri, 22 Mar 2019 at 12:48, Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> wrote: > >> exynos_core_restart() is called by secondary CPU boot procedure, used by > >> CPU hotplug. Replace of_machine_is_compatible() call with a simple SoC > >> revision check. > >> > >> of_machine_is_compatible() function performs a dozen of string comparisons > >> during the full device tree walk, while soc_is_exynos3250() is a simple > >> integer check on SoC revision variable. > > Yes but it is against the effort of getting rid of all soc_is_() (see > > https://patchwork.kernel.org/project/linux-samsung-soc/list/?series=43565&state=* > > ). It also makes this code sticky to mach - we cannot move it to > > drivers. See also Arnd's opinion: > > https://marc.info/?l=devicetree&m=139291569126848&w=2 > > > > Did you measure the practical performance impact of this change? > > No, I didn't measure the performance, but recently I noticed the > following warning: > > ============================= > WARNING: suspicious RCU usage > 5.10.0-rc1-00001-g6f65599d1f4f-dirty #1800 Not tainted > ----------------------------- > ./include/trace/events/lock.h:37 suspicious rcu_dereference_check() usage! > > other info that might help us debug this: > > > rcu_scheduler_active = 2, debug_locks = 1 > RCU used illegally from extended quiescent state! > no locks held by swapper/0/0. > > stack backtrace: > CPU: 0 PID: 0 Comm: swapper/0 Not tainted > 5.10.0-rc1-00001-g6f65599d1f4f-dirty #1800 > Hardware name: Samsung Exynos (Flattened Device Tree) > [<c0111514>] (unwind_backtrace) from [<c010ceb8>] (show_stack+0x10/0x14) > [<c010ceb8>] (show_stack) from [<c0b1d8dc>] (dump_stack+0xb4/0xd4) > [<c0b1d8dc>] (dump_stack) from [<c0194acc>] (lock_acquire+0x418/0x584) > [<c0194acc>] (lock_acquire) from [<c0b29e58>] > (_raw_spin_lock_irqsave+0x4c/0x60) > [<c0b29e58>] (_raw_spin_lock_irqsave) from [<c0897af4>] > (of_device_is_compatible+0x1c/0x4c) > [<c0897af4>] (of_device_is_compatible) from [<c01216d8>] > (exynos_core_restart+0x14/0xb0) > [<c01216d8>] (exynos_core_restart) from [<c0120a78>] > (exynos_cpu0_enter_aftr+0x1d0/0x1dc) > [<c0120a78>] (exynos_cpu0_enter_aftr) from [<c08575b0>] > (exynos_enter_coupled_lowpower+0x44/0x74) > [<c08575b0>] (exynos_enter_coupled_lowpower) from [<c085477c>] > (cpuidle_enter_state+0x178/0x660) > [<c085477c>] (cpuidle_enter_state) from [<c08572dc>] > (cpuidle_enter_state_coupled+0x35c/0x378) > [<c08572dc>] (cpuidle_enter_state_coupled) from [<c0854cc8>] > (cpuidle_enter+0x50/0x54) > [<c0854cc8>] (cpuidle_enter) from [<c0164854>] (do_idle+0x224/0x2a4) > [<c0164854>] (do_idle) from [<c0164c88>] (cpu_startup_entry+0x18/0x1c) > [<c0164c88>] (cpu_startup_entry) from [<c1100fa0>] > (start_kernel+0x640/0x67c) > [<c1100fa0>] (start_kernel) from [<00000000>] (0x0) > > I will add this to the commit message and resend. This looks like a good > reason for this change. Good point, thanks. Best regards, Krzysztof
