From: Peter Zijlstra <peterz@infradead.org> To: Paul Mundt <lethal@linux-sh.org> Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>, Daniel Walker <dwalker@fifo99.com>, Linus Walleij <linus.ml.walleij@gmail.com>, Andrew Victor <linux@maxim.org.za>, Haavard Skinnemoen <hskinnemoen@atmel.com>, Andrew Morton <akpm@linux-foundation.org>, John Stultz <johnstul@linux.vnet.ibm.com>, linux-arm-kernel@lists.arm.linux.org.uk, linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched: sched_clock() clocksource handling. Date: Tue, 02 Jun 2009 07:41:35 +0000 [thread overview] Message-ID: <1243928495.23657.5642.camel@twins> (raw) In-Reply-To: <20090602073515.GB17710@linux-sh.org> On Tue, 2009-06-02 at 16:35 +0900, Paul Mundt wrote: > > We already do via select_clocksource(), if we are unregistering the > current one then a new one with the flag set is selected. Before that, > the override is likewise given preference, and we fall back on jiffies if > there is nothing else. I suppose we could try and find the "best" one, > but I think the override and manual clocksource selection should be fine > for this. Ah, ok. So unregister calls select_clocksource again? That does leave us a small window with jiffies, but I guess that's ok. > Now that you mention it though, the sched_clocksource() assignment within > select_clocksource() happens underneath the clocksource_lock, but is not > using rcu_assign_pointer(). Right, that would want fixing indeed. > If the assignment there needs to use > rcu_assign_pointer() then presumably all of the unlock paths that do > select_clocksource() will have to synchronize_rcu()? No, you only have to do sync_rcu() when stuff that could have referenced is going away and you cannot use call_rcu(). So when selecting a new clocksource, you don't need synchonization because stuff doesn't go away (I think :-)
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From: Peter Zijlstra <peterz@infradead.org> To: Paul Mundt <lethal@linux-sh.org> Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>, Daniel Walker <dwalker@fifo99.com>, Linus Walleij <linus.ml.walleij@gmail.com>, Andrew Victor <linux@maxim.org.za>, Haavard Skinnemoen <hskinnemoen@atmel.com>, Andrew Morton <akpm@linux-foundation.org>, John Stultz <johnstul@linux.vnet.ibm.com>, linux-arm-kernel@lists.arm.linux.org.uk, linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched: sched_clock() clocksource handling. Date: Tue, 02 Jun 2009 09:41:35 +0200 [thread overview] Message-ID: <1243928495.23657.5642.camel@twins> (raw) In-Reply-To: <20090602073515.GB17710@linux-sh.org> On Tue, 2009-06-02 at 16:35 +0900, Paul Mundt wrote: > > We already do via select_clocksource(), if we are unregistering the > current one then a new one with the flag set is selected. Before that, > the override is likewise given preference, and we fall back on jiffies if > there is nothing else. I suppose we could try and find the "best" one, > but I think the override and manual clocksource selection should be fine > for this. Ah, ok. So unregister calls select_clocksource again? That does leave us a small window with jiffies, but I guess that's ok. > Now that you mention it though, the sched_clocksource() assignment within > select_clocksource() happens underneath the clocksource_lock, but is not > using rcu_assign_pointer(). Right, that would want fixing indeed. > If the assignment there needs to use > rcu_assign_pointer() then presumably all of the unlock paths that do > select_clocksource() will have to synchronize_rcu()? No, you only have to do sync_rcu() when stuff that could have referenced is going away and you cannot use call_rcu(). So when selecting a new clocksource, you don't need synchonization because stuff doesn't go away (I think :-)
next prev parent reply other threads:[~2009-06-02 7:41 UTC|newest] Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top 2009-06-02 7:17 [PATCH] sched: sched_clock() clocksource handling Paul Mundt 2009-06-02 7:17 ` Paul Mundt 2009-06-02 7:25 ` Peter Zijlstra 2009-06-02 7:25 ` Peter Zijlstra 2009-06-02 7:35 ` Paul Mundt 2009-06-02 7:35 ` Paul Mundt 2009-06-02 7:41 ` Peter Zijlstra [this message] 2009-06-02 7:41 ` Peter Zijlstra 2009-06-02 7:54 ` Paul Mundt 2009-06-02 7:54 ` Paul Mundt 2009-06-02 8:00 ` Peter Zijlstra 2009-06-02 8:00 ` Peter Zijlstra 2009-06-02 8:00 ` Paul Mundt 2009-06-02 8:00 ` Paul Mundt 2009-06-02 11:49 ` Daniel Walker 2009-06-02 11:49 ` Daniel Walker 2009-06-02 20:21 ` Thomas Gleixner 2009-06-02 20:21 ` Thomas Gleixner 2009-06-03 3:36 ` Paul Mundt 2009-06-03 3:36 ` Paul Mundt 2009-06-03 14:58 ` Daniel Walker 2009-06-03 14:58 ` Daniel Walker 2009-06-02 12:26 ` Peter Zijlstra 2009-06-02 12:26 ` Peter Zijlstra 2009-06-02 20:17 ` Thomas Gleixner 2009-06-02 20:17 ` Thomas Gleixner 2009-06-03 3:39 ` Paul Mundt 2009-06-03 3:39 ` Paul Mundt 2009-06-02 14:17 ` Rabin Vincent 2009-06-02 14:29 ` Rabin Vincent 2009-06-02 14:25 ` Peter Zijlstra 2009-06-02 14:25 ` Peter Zijlstra 2009-06-02 22:24 ` john stultz 2009-06-02 22:24 ` john stultz 2009-06-03 7:03 ` Peter Zijlstra 2009-06-03 7:03 ` Peter Zijlstra
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