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 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
