From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 6/6] arm64: mm: Enable RCU fast_gup
Date: Thu, 26 Jun 2014 09:56:05 +0200
Message-ID: <20140626075605.GB12054@laptop.lan>
References: <1403710824-24340-1-git-send-email-steve.capper@linaro.org>
 <1403710824-24340-7-git-send-email-steve.capper@linaro.org>
 <20140625165003.GI15240@leverpostej>
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To: Mark Rutland <mark.rutland@arm.com>
Cc: Steve Capper <steve.capper@linaro.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, Catalin Marinas <Catalin.Marinas@arm.com>, "linux@arm.linux.org.uk" <linux@arm.linux.org.uk>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "anders.roxell@linaro.org" <anders.roxell@linaro.org>, "gary.robertson@linaro.org" <gary.robertson@linaro.org>, Will Deacon <Will.Deacon@arm.com>, "akpm@linux-foundation.org" <akpm@linux-foundation.org>, "christoffer.dall@linaro.org" <christoffer.dall@linaro.org>, Thomas Gleixner <tglx@linutronix.de>
List-Id: linux-arch.vger.kernel.org

On Wed, Jun 25, 2014 at 05:50:03PM +0100, Mark Rutland wrote:
> Hi Steve,
> 
> On Wed, Jun 25, 2014 at 04:40:24PM +0100, Steve Capper wrote:
> > Activate the RCU fast_gup for ARM64. We also need to force THP splits
> > to broadcast an IPI s.t. we block in the fast_gup page walker. As THP
> > splits are comparatively rare, this should not lead to a noticeable
> > performance degradation.
> > 
> > Some pre-requisite functions pud_write and pud_page are also added.
> > 
> > Signed-off-by: Steve Capper <steve.capper@linaro.org>
> > ---
> >  arch/arm64/Kconfig               |  3 +++
> >  arch/arm64/include/asm/pgtable.h | 11 ++++++++++-
> >  arch/arm64/mm/flush.c            | 19 +++++++++++++++++++
> >  3 files changed, 32 insertions(+), 1 deletion(-)
> 
> [...]
> 
> > diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> > index e4193e3..ddf96c1 100644
> > --- a/arch/arm64/mm/flush.c
> > +++ b/arch/arm64/mm/flush.c
> > @@ -103,3 +103,22 @@ EXPORT_SYMBOL(flush_dcache_page);
> >   */
> >  EXPORT_SYMBOL(flush_cache_all);
> >  EXPORT_SYMBOL(flush_icache_range);
> > +
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +#ifdef CONFIG_HAVE_RCU_TABLE_FREE
> > +static void thp_splitting_flush_sync(void *arg)
> > +{
> > +}
> > +
> > +void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
> > +			  pmd_t *pmdp)
> > +{
> > +	pmd_t pmd = pmd_mksplitting(*pmdp);
> > +	VM_BUG_ON(address & ~PMD_MASK);
> > +	set_pmd_at(vma->vm_mm, address, pmdp, pmd);
> > +
> > +	/* dummy IPI to serialise against fast_gup */
> > +	smp_call_function(thp_splitting_flush_sync, NULL, 1);
> 
> Is there some reason we can't use kick_all_cpus_sync()?

Yes that would be equivalent. But looking at that, I worry about the
smp_mb(); archs are supposed to make sure IPIs are serializing.

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From mboxrd@z Thu Jan  1 00:00:00 1970
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	<rfc822;linux-arch@vger.kernel.org>); Thu, 26 Jun 2014 03:56:15 -0400
Date: Thu, 26 Jun 2014 09:56:05 +0200
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 6/6] arm64: mm: Enable RCU fast_gup
Message-ID: <20140626075605.GB12054@laptop.lan>
References: <1403710824-24340-1-git-send-email-steve.capper@linaro.org>
 <1403710824-24340-7-git-send-email-steve.capper@linaro.org>
 <20140625165003.GI15240@leverpostej>
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Sender: linux-arch-owner@vger.kernel.org
List-ID: <linux-arch.vger.kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Steve Capper <steve.capper@linaro.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, Catalin Marinas <Catalin.Marinas@arm.com>, "linux@arm.linux.org.uk" <linux@arm.linux.org.uk>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "anders.roxell@linaro.org" <anders.roxell@linaro.org>, "gary.robertson@linaro.org" <gary.robertson@linaro.org>, Will Deacon <Will.Deacon@arm.com>, "akpm@linux-foundation.org" <akpm@linux-foundation.org>, "christoffer.dall@linaro.org" <christoffer.dall@linaro.org>, Thomas Gleixner <tglx@linutronix.de>
Message-ID: <20140626075605.1A_4FjpmoJdW5Q40JSnRA-IFcK2Q1v6pH0oMcH0tQwQ@z>

On Wed, Jun 25, 2014 at 05:50:03PM +0100, Mark Rutland wrote:
> Hi Steve,
> 
> On Wed, Jun 25, 2014 at 04:40:24PM +0100, Steve Capper wrote:
> > Activate the RCU fast_gup for ARM64. We also need to force THP splits
> > to broadcast an IPI s.t. we block in the fast_gup page walker. As THP
> > splits are comparatively rare, this should not lead to a noticeable
> > performance degradation.
> > 
> > Some pre-requisite functions pud_write and pud_page are also added.
> > 
> > Signed-off-by: Steve Capper <steve.capper@linaro.org>
> > ---
> >  arch/arm64/Kconfig               |  3 +++
> >  arch/arm64/include/asm/pgtable.h | 11 ++++++++++-
> >  arch/arm64/mm/flush.c            | 19 +++++++++++++++++++
> >  3 files changed, 32 insertions(+), 1 deletion(-)
> 
> [...]
> 
> > diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> > index e4193e3..ddf96c1 100644
> > --- a/arch/arm64/mm/flush.c
> > +++ b/arch/arm64/mm/flush.c
> > @@ -103,3 +103,22 @@ EXPORT_SYMBOL(flush_dcache_page);
> >   */
> >  EXPORT_SYMBOL(flush_cache_all);
> >  EXPORT_SYMBOL(flush_icache_range);
> > +
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +#ifdef CONFIG_HAVE_RCU_TABLE_FREE
> > +static void thp_splitting_flush_sync(void *arg)
> > +{
> > +}
> > +
> > +void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
> > +			  pmd_t *pmdp)
> > +{
> > +	pmd_t pmd = pmd_mksplitting(*pmdp);
> > +	VM_BUG_ON(address & ~PMD_MASK);
> > +	set_pmd_at(vma->vm_mm, address, pmdp, pmd);
> > +
> > +	/* dummy IPI to serialise against fast_gup */
> > +	smp_call_function(thp_splitting_flush_sync, NULL, 1);
> 
> Is there some reason we can't use kick_all_cpus_sync()?

Yes that would be equivalent. But looking at that, I worry about the
smp_mb(); archs are supposed to make sure IPIs are serializing.


From mboxrd@z Thu Jan  1 00:00:00 1970
From: peterz@infradead.org (Peter Zijlstra)
Date: Thu, 26 Jun 2014 09:56:05 +0200
Subject: [PATCH 6/6] arm64: mm: Enable RCU fast_gup
In-Reply-To: <20140625165003.GI15240@leverpostej>
References: <1403710824-24340-1-git-send-email-steve.capper@linaro.org>
 <1403710824-24340-7-git-send-email-steve.capper@linaro.org>
 <20140625165003.GI15240@leverpostej>
Message-ID: <20140626075605.GB12054@laptop.lan>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wed, Jun 25, 2014 at 05:50:03PM +0100, Mark Rutland wrote:
> Hi Steve,
> 
> On Wed, Jun 25, 2014 at 04:40:24PM +0100, Steve Capper wrote:
> > Activate the RCU fast_gup for ARM64. We also need to force THP splits
> > to broadcast an IPI s.t. we block in the fast_gup page walker. As THP
> > splits are comparatively rare, this should not lead to a noticeable
> > performance degradation.
> > 
> > Some pre-requisite functions pud_write and pud_page are also added.
> > 
> > Signed-off-by: Steve Capper <steve.capper@linaro.org>
> > ---
> >  arch/arm64/Kconfig               |  3 +++
> >  arch/arm64/include/asm/pgtable.h | 11 ++++++++++-
> >  arch/arm64/mm/flush.c            | 19 +++++++++++++++++++
> >  3 files changed, 32 insertions(+), 1 deletion(-)
> 
> [...]
> 
> > diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> > index e4193e3..ddf96c1 100644
> > --- a/arch/arm64/mm/flush.c
> > +++ b/arch/arm64/mm/flush.c
> > @@ -103,3 +103,22 @@ EXPORT_SYMBOL(flush_dcache_page);
> >   */
> >  EXPORT_SYMBOL(flush_cache_all);
> >  EXPORT_SYMBOL(flush_icache_range);
> > +
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +#ifdef CONFIG_HAVE_RCU_TABLE_FREE
> > +static void thp_splitting_flush_sync(void *arg)
> > +{
> > +}
> > +
> > +void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
> > +			  pmd_t *pmdp)
> > +{
> > +	pmd_t pmd = pmd_mksplitting(*pmdp);
> > +	VM_BUG_ON(address & ~PMD_MASK);
> > +	set_pmd_at(vma->vm_mm, address, pmdp, pmd);
> > +
> > +	/* dummy IPI to serialise against fast_gup */
> > +	smp_call_function(thp_splitting_flush_sync, NULL, 1);
> 
> Is there some reason we can't use kick_all_cpus_sync()?

Yes that would be equivalent. But looking at that, I worry about the
smp_mb(); archs are supposed to make sure IPIs are serializing.