From mboxrd@z Thu Jan 1 00:00:00 1970 From: thunder.leizhen@huawei.com (Leizhen (ThunderTown)) Date: Mon, 26 Jun 2017 21:41:47 +0800 Subject: [PATCH 1/1] iommu/arm-smmu-v3: replace writel with writel_relaxed in queue_inc_prod In-Reply-To: <59510C20.6000300@huawei.com> References: <1497956694-11784-1-git-send-email-thunder.leizhen@huawei.com> <5949CBB7.1030908@huawei.com> <20170621090803.GB3768@arm.com> <59510C20.6000300@huawei.com> Message-ID: <59510F1B.60304@huawei.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 2017/6/26 21:29, Leizhen (ThunderTown) wrote: > > > On 2017/6/21 17:08, Will Deacon wrote: >> On Wed, Jun 21, 2017 at 09:28:23AM +0800, Leizhen (ThunderTown) wrote: >>> On 2017/6/20 19:35, Robin Murphy wrote: >>>> On 20/06/17 12:04, Zhen Lei wrote: >>>>> This function is protected by spinlock, and the latter will do memory >>>>> barrier implicitly. So that we can safely use writel_relaxed. In fact, the >>>>> dmb operation will lengthen the time protected by lock, which indirectly >>>>> increase the locking confliction in the stress scene. >>>> >>>> If you remove the DSB between writing the commands (to Normal memory) >>>> and writing the pointer (to Device memory), how can you guarantee that >>>> the complete command is visible to the SMMU and it isn't going to try to >>>> consume stale memory contents? The spinlock is irrelevant since it's >>>> taken *before* the command is written. >>> OK, I see, thanks. Let's me see if there are any other methods. And I think >>> that this may should be done well by hardware. >> >> FWIW, I did use the _relaxed variants wherever I could when I wrote the >> driver. There might, of course, be bugs, but it's not like the normal case >> for drivers where the author didn't consider the _relaxed accessors >> initially. > A good news. I got a new idea and I will post v2 later. [PATCH 0/5] arm-smmu: performance optimization [PATCH 1/5] iommu/arm-smmu-v3: put off the execution of TLBI* to reduce lock confliction I just sent. > >> >> Will >> >> . >> > -- Thanks! BestRegards