From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH 3/7] iommu/arm-smmu: Work around MMU-500 prefetch errata Date: Thu, 21 Apr 2016 17:15:53 +0100 Message-ID: <20160421161552.GI929@arm.com> References: <0484444b6257bfb6adb68405a72c64fc4fc98142.1460391217.git.robin.murphy@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <0484444b6257bfb6adb68405a72c64fc4fc98142.1460391217.git.robin.murphy-5wv7dgnIgG8@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Robin Murphy Cc: Catalin Marinas , iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, tchalamarla-M3mlKVOIwJVv6pq1l3V1OdBPR1lH4CV8@public.gmane.org, brian.starkey-5wv7dgnIgG8@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: iommu@lists.linux-foundation.org On Wed, Apr 13, 2016 at 06:12:59PM +0100, Robin Murphy wrote: > MMU-500 erratum #841119 is tickled by a particular set of circumstances > interacting with the next-page prefetcher. Since said prefetcher is > quite dumb and actually detrimental to performance in some cases (by > causing unwanted TLB evictions for non-sequential access patterns), we > lose very little by turning it off, and what we gain is a guarantee that > the erratum is never hit. > > As a bonus, the same workaround will also prevent erratum #826419 once > v7 short descriptor support is implemented. > > CC: Catalin Marinas > CC: Will Deacon > Signed-off-by: Robin Murphy > --- > Documentation/arm64/silicon-errata.txt | 1 + > drivers/iommu/arm-smmu.c | 16 +++++++++++++++- > 2 files changed, 16 insertions(+), 1 deletion(-) Looks fine, but can you update silicon-errata.txt too, please? It's a handy reference for "what is Linux actively working around" and this one is somewhat hidden away. Will From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Thu, 21 Apr 2016 17:15:53 +0100 Subject: [PATCH 3/7] iommu/arm-smmu: Work around MMU-500 prefetch errata In-Reply-To: <0484444b6257bfb6adb68405a72c64fc4fc98142.1460391217.git.robin.murphy@arm.com> References: <0484444b6257bfb6adb68405a72c64fc4fc98142.1460391217.git.robin.murphy@arm.com> Message-ID: <20160421161552.GI929@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Apr 13, 2016 at 06:12:59PM +0100, Robin Murphy wrote: > MMU-500 erratum #841119 is tickled by a particular set of circumstances > interacting with the next-page prefetcher. Since said prefetcher is > quite dumb and actually detrimental to performance in some cases (by > causing unwanted TLB evictions for non-sequential access patterns), we > lose very little by turning it off, and what we gain is a guarantee that > the erratum is never hit. > > As a bonus, the same workaround will also prevent erratum #826419 once > v7 short descriptor support is implemented. > > CC: Catalin Marinas > CC: Will Deacon > Signed-off-by: Robin Murphy > --- > Documentation/arm64/silicon-errata.txt | 1 + > drivers/iommu/arm-smmu.c | 16 +++++++++++++++- > 2 files changed, 16 insertions(+), 1 deletion(-) Looks fine, but can you update silicon-errata.txt too, please? It's a handy reference for "what is Linux actively working around" and this one is somewhat hidden away. Will