From mboxrd@z Thu Jan 1 00:00:00 1970 From: David F Barrera Subject: Re: [PATCH] UNTESTED backport rcu_needs_cpu and call it from stop_hz_timer UNTESTED Date: Fri, 09 Jun 2006 18:45:31 -0500 Message-ID: <448A081B.5070509@us.ibm.com> References: <1149884488.9498.11.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1149884488.9498.11.camel@localhost.localdomain> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Harry Butterworth Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org Harry Butterworth wrote: > THIS PATCH FOR REVIEW ONLY IT'S UNTESTED!!!!!! Ill test on Monday if > no-one has done it by then. > > There is a problem with the current implementation of stop_hz_timer in > arch/i386/kernel/time-xen.c where the hz timer can be stopped on a CPU > which has RCU callbacks pending. > > This patch backports a new RCU API created to fix this problem for the > s390 implementation of stop_hz_timer and also updates the time-xen.c > implementation of stop_hz_timer to call the new API. > > Signed-off-by: Harry Butterworth > > > ------------------------------------------------------------------------ > > diff -r 8c64169a05d3 -r 8ef455f268b3 linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c > --- a/linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c Thu Jun 8 08:52:04 2006 > +++ b/linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c Fri Jun 9 19:47:18 2006 > @@ -978,12 +978,19 @@ > unsigned int cpu = smp_processor_id(); > unsigned long j; > > - /* We must do this /before/ checking rcu_pending(). */ > cpu_set(cpu, nohz_cpu_mask); > + > + /* See matching smp_mb in rcu_start_batch in rcupdate.c. These mbs */ > + /* ensure that if __rcu_pending (nested in rcu_needs_cpu) fetches a */ > + /* value of rcp->cur that matches rdp->quiescbatch and allows us to */ > + /* stop the hz timer then the cpumasks created for subsequent values */ > + /* of cur in rcu_start_batch are guaranteed to pick up the updated */ > + /* nohz_cpu_mask and so will not depend on this cpu. */ > + > smp_mb(); > > /* Leave ourselves in 'tick mode' if rcu or softirq pending. */ > - if (rcu_pending(cpu) || local_softirq_pending()) { > + if (rcu_needs_cpu(cpu) || local_softirq_pending()) { > cpu_clear(cpu, nohz_cpu_mask); > j = jiffies + 1; > } else { > diff -r 8c64169a05d3 -r 8ef455f268b3 patches/linux-2.6.16.13/rcu_needs_cpu.patch > --- /dev/null Thu Jun 8 08:52:04 2006 > +++ b/patches/linux-2.6.16.13/rcu_needs_cpu.patch Fri Jun 9 19:47:18 2006 > @@ -0,0 +1,33 @@ > +--- ../pristine-linux-2.6.16.13/kernel/rcupdate.c 2006-05-02 22:38:44.000000000 +0100 > ++++ ./kernel/rcupdate.c 2006-06-09 20:27:45.000000000 +0100 > +@@ -485,6 +485,20 @@ int rcu_pending(int cpu) > + __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu)); > + } > + > ++/* > ++ * Check to see if any future RCU-related work will need to be done > ++ * by the current CPU, even if none need be done immediately, returning > ++ * 1 if so. This function is part of the RCU implementation; it is -not- > ++ * an exported member of the RCU API. > ++ */ > ++int rcu_needs_cpu(int cpu) > ++{ > ++ struct rcu_data *rdp = &per_cpu(rcu_data, cpu); > ++ struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu); > ++ > ++ return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu)); > ++} > ++ > + void rcu_check_callbacks(int cpu, int user) > + { > + if (user || > +--- ../pristine-linux-2.6.16.13/include/linux/rcupdate.h 2006-05-02 22:38:44.000000000 +0100 > ++++ ./include/linux/rcupdate.h 2006-06-09 20:28:57.000000000 +0100 > +@@ -134,6 +134,7 @@ static inline void rcu_bh_qsctr_inc(int > + } > + > + extern int rcu_pending(int cpu); > ++extern int rcu_needs_cpu(int cpu); > + > + /** > + * rcu_read_lock - mark the beginning of an RCU read-side critical section. > > ------------------------------------------------------------------------ > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel > Harry, I am doing some quick testing of your patch. So far, the results are consistent with the mainline testing results. -- Regards, David F Barrera Linux Technology Center Systems and Technology Group, IBM "The wisest men follow their own direction. " Euripides