Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756469Ab1D3M7c (ORCPT ); Sat, 30 Apr 2011 08:59:32 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:58830 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752838Ab1D3M7a (ORCPT ); Sat, 30 Apr 2011 08:59:30 -0400 Date: Sat, 30 Apr 2011 05:59:28 -0700 From: "Paul E. McKenney" To: Gleb Natapov Cc: linux-kernel@vger.kernel.org, avi@redhat.com, mtosatti@redhat.com, kvm@vger.kernel.org Subject: Re: [PATCH 1/2] rcu: export rcu_note_context_switch() function Message-ID: <20110430125928.GJ2297@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1303984323-3203-1-git-send-email-gleb@redhat.com> <1303984323-3203-2-git-send-email-gleb@redhat.com> <20110429083618.GL2191@linux.vnet.ibm.com> <20110429083904.GA12987@linux.vnet.ibm.com> <20110429180239.GA32566@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110429180239.GA32566@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4121 Lines: 103 On Fri, Apr 29, 2011 at 09:02:39PM +0300, Gleb Natapov wrote: > On Fri, Apr 29, 2011 at 01:39:04AM -0700, Paul E. McKenney wrote: > > On Fri, Apr 29, 2011 at 01:36:18AM -0700, Paul E. McKenney wrote: > > > On Thu, Apr 28, 2011 at 12:52:02PM +0300, Gleb Natapov wrote: > > > > > > Hmmm.... This is interesting. KVM being a module, we either expand > > > TINY_RCU's size a bit by making rcu_note_context_switch() be a real > > > function in rcutiny.c and adding an export, or we expand it by adding > > > two exports. > > > > > > I would like to solve this without making TINY_RCU larger, and preferably > > > by making it smaller. Any ideas come to mind? (Other than making > > > KVM depend on CONFIG_SMP, which sounds too much like throwing out the > > > baby with the bathwater.) > > > > Nothing quite like hitting "send" to make an idea show up... > > > > In a UP kernel, does it actually help anything to have KVM > > tell RCU about executing in a guest? If not, could we have a > > rcu_note_context_switch_kvm() that is a static inline empty function in > > TINY_RCU and maps to rcu_note_context_switch() for TREE_RCU? > > > That will work, but does making rcu_note_context_switch() out of line > actually increase kernel size? The function is called in two places > currently, so by making it out of line we make two calling site smaller. > Will measure it next week. One thing to keep in mind... Calling an out-of-line function from KVM requires an export, each of which significantly increases TINY_RCU's memory footprint. Thanx, Paul > > > > Signed-off-by: Gleb Natapov > > > > --- > > > > include/linux/rcutiny.h | 6 +----- > > > > kernel/rcutiny.c | 7 +++++++ > > > > kernel/rcutree.c | 1 + > > > > 3 files changed, 9 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h > > > > index 30ebd7c..8e5f7cf 100644 > > > > --- a/include/linux/rcutiny.h > > > > +++ b/include/linux/rcutiny.h > > > > @@ -93,11 +93,7 @@ static inline int rcu_needs_cpu(int cpu) > > > > > > > > #endif /* #else #ifdef CONFIG_TINY_RCU */ > > > > > > > > -static inline void rcu_note_context_switch(int cpu) > > > > -{ > > > > - rcu_sched_qs(cpu); > > > > - rcu_preempt_note_context_switch(); > > > > -} > > > > +extern void rcu_note_context_switch(int cpu); > > > > > > > > /* > > > > * Return the number of grace periods. > > > > diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c > > > > index 0c343b9..3d715a4 100644 > > > > --- a/kernel/rcutiny.c > > > > +++ b/kernel/rcutiny.c > > > > @@ -78,6 +78,13 @@ void rcu_exit_nohz(void) > > > > > > > > #endif /* #ifdef CONFIG_NO_HZ */ > > > > > > > > +void rcu_note_context_switch(int cpu) > > > > +{ > > > > + rcu_sched_qs(cpu); > > > > + rcu_preempt_note_context_switch(); > > > > +} > > > > +EXPORT_SYMBOL_GPL(rcu_note_context_switch); > > > > + > > > > /* > > > > * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc(). > > > > * Also disable irqs to avoid confusion due to interrupt handlers > > > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > > > index dd4aea8..0837d63 100644 > > > > --- a/kernel/rcutree.c > > > > +++ b/kernel/rcutree.c > > > > @@ -124,6 +124,7 @@ void rcu_note_context_switch(int cpu) > > > > rcu_sched_qs(cpu); > > > > rcu_preempt_note_context_switch(cpu); > > > > } > > > > +EXPORT_SYMBOL_GPL(rcu_note_context_switch); > > > > > > > > #ifdef CONFIG_NO_HZ > > > > DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { > > > > -- > > > > 1.7.2.3 > > > > > > > > -- > > > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > > > the body of a message to majordomo@vger.kernel.org > > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > Please read the FAQ at http://www.tux.org/lkml/ > > -- > Gleb. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/