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McKenney" Cc: Sergey Senozhatsky , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , Suleiman Souhlal , rcu@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] rcu/tree: consider time a VM was suspended Message-ID: References: <20210516102716.689596-1-senozhatsky@chromium.org> <20210517162312.GG4441@paulmck-ThinkPad-P17-Gen-1> <20210518231514.GS4441@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210518231514.GS4441@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On (21/05/18 16:15), Paul E. McKenney wrote: > > In the shorter term... PVCLOCK_GUEST_STOPPED is mostly for things like > guest migration and debugger breakpoints, correct? Either way, I am > wondering if rcu_cpu_stall_reset() should take a lighter touch. Right > now, it effectively disables all stalls for the current grace period. > Why not make it restart the stall timeout when the stoppage is detected? rcu_cpu_stall_reset() is used in many other places, not sure if we can change its behaviour rcu_cpu_stall_reset(). Maybe it'll be possible to just stop calling it from PV-clock and do something like this --- diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c index eda37df016f0..2d2489eda8e6 100644 --- a/arch/x86/kernel/pvclock.c +++ b/arch/x86/kernel/pvclock.c @@ -40,7 +40,7 @@ void pvclock_touch_watchdogs(void) { touch_softlockup_watchdog_sync(); clocksource_touch_watchdog(); - rcu_cpu_stall_reset(); + record_gp_stall_check_time(); reset_hung_task_detector(); } diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index cb233c79f0bc..6b3165c7a2c3 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -137,7 +137,7 @@ void rcu_cpu_stall_reset(void) // Interaction with RCU grace periods /* Start of new grace period, so record stall time (and forcing times). */ -static void record_gp_stall_check_time(void) +void record_gp_stall_check_time(void) { unsigned long j = jiffies; unsigned long j1;