Messages in this thread | | | Date | Sun, 15 Jan 2017 01:24:54 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering |
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On Sun, Jan 15, 2017 at 08:57:11AM +0100, Ingo Molnar wrote: > > * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > > > On Sun, Jan 15, 2017 at 08:11:23AM +0100, Ingo Molnar wrote: > > > > > > * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > > > > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > > > index 357b32aaea48..5fdfe874229e 100644 > > > > --- a/include/linux/rcupdate.h > > > > +++ b/include/linux/rcupdate.h > > > > @@ -1175,11 +1175,11 @@ do { \ > > > > * if the UNLOCK and LOCK are executed by the same CPU or if the > > > > * UNLOCK and LOCK operate on the same lock variable. > > > > */ > > > > -#ifdef CONFIG_PPC > > > > +#ifdef CONFIG_ARCH_WEAK_RELACQ > > > > #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ > > > > -#else /* #ifdef CONFIG_PPC */ > > > > +#else /* #ifdef CONFIG_ARCH_WEAK_RELACQ */ > > > > #define smp_mb__after_unlock_lock() do { } while (0) > > > > -#endif /* #else #ifdef CONFIG_PPC */ > > > > +#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELACQ */ > > > > > > > > > > > > > > So at the risk of sounding totally pedantic, why not structure it like the > > > existing smp_mb__before/after*() primitives in barrier.h? > > > > > > That allows asm-generic/barrier.h to pick up the definition - for example in the > > > case of smp_acquire__after_ctrl_dep() we do: > > > > > > #ifndef smp_acquire__after_ctrl_dep > > > #define smp_acquire__after_ctrl_dep() smp_rmb() > > > #endif > > > > > > Which allows Tile to relax it: > > > > > > arch/tile/include/asm/barrier.h:#define smp_acquire__after_ctrl_dep() barrier() > > > > > > I.e. I'd move the API definition out of rcupdate.h and into barrier.h - even > > > though tree-RCU is the only user of this barrier type. > > > > I wouldn't have any problem with that, however, some time back it was > > moved into RCU because (you guessed it!) RCU is the only user. ;-) > > Indeed ... > > [sounds of rummaging around in the Git tree] > > I found this commit of yours from ancient history (more than a year ago!): > > commit 12d560f4ea87030667438a169912380be00cea4b > Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Date: Tue Jul 14 18:35:23 2015 -0700 > > rcu,locking: Privatize smp_mb__after_unlock_lock() > > RCU is the only thing that uses smp_mb__after_unlock_lock(), and is > likely the only thing that ever will use it, so this commit makes this > macro private to RCU. > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Cc: Will Deacon <will.deacon@arm.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> > Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org> > > So I concur and I'm fine with your patch - or with the status quo code as well.
I already have the patch queued, so how about I keep it if I get an ack from the powerpc guys and drop it otherwise?
Thanx, Paul
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