From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [RFC PATCH] Introduce timekeeper latch synchronization Date: Fri, 13 Sep 2013 11:30:20 -0400 Message-ID: <20130913153020.GA24383@Krystal> References: <20130913025253.GA17218@Krystal> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20130913025253.GA17218@Krystal> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra Cc: "Paul E. McKenney" , John Stultz , Thomas Gleixner , Richard Cochran , Prarit Bhargava , Greg Kroah-Hartman , Steven Rostedt , Ingo Molnar , linux-kernel@vger.kernel.org, lttng-dev@lists.lttng.org List-Id: lttng-dev@lists.lttng.org * Mathieu Desnoyers (mathieu.desnoyers@efficios.com) wrote: [...] > @@ -1362,29 +1398,31 @@ static inline void old_vsyscall_fixup(struct timekeeper *tk) > static void update_wall_time(void) > { [...] > - /* > - * Update the real timekeeper. > - * > - * We could avoid this memcpy by switching pointers, but that > - * requires changes to all other timekeeper usage sites as > - * well, i.e. move the timekeeper pointer getter into the > - * spinlocked/seqcount protected sections. And we trade this > - * memcpy under the timekeeper_seq against one before we start > - * updating. > - */ > - memcpy(real_tk, tk, sizeof(*tk)); > - timekeeping_update(real_tk, action); This line above appears to be important ;-) Let's see if my screensaver stops misbehaving if I put it back. I will of course send a v2 after some more testing. By the way, if there are some standard test-bench for timekeeping, I'd be very interested to hear about them. Thanks! Mathieu > - write_seqcount_end(&timekeeper_seq); > out: > + timekeeper_write_end(&latch_timekeeper); > raw_spin_unlock_irqrestore(&timekeeper_lock, flags); > } -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com