linux-kernel - Re: [PATCH 0/5] arm-smmu: performance optimization

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Date:   Fri, 18 Aug 2017 11:19:00 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Will Deacon <will.deacon@....com>
CC:     Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        Robin Murphy <robin.murphy@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Zefan Li <lizefan@...wei.com>, Xinwei Hu <huxinwei@...wei.com>,
        Tianhong Ding <dingtianhong@...wei.com>,
        Hanjun Guo <guohanjun@...wei.com>,
        John Garry <john.garry@...wei.com>, <nwatters@...eaurora.org>
Subject: Re: [PATCH 0/5] arm-smmu: performance optimization



On 2017/8/17 22:36, Will Deacon wrote:
> Thunder, Nate, Robin,
> 
> On Mon, Jun 26, 2017 at 09:38:45PM +0800, Zhen Lei wrote:
>> I described the optimization more detail in patch 1 and 2, and patch 3-5 are
>> the implementation on arm-smmu/arm-smmu-v3 of patch 2.
>>
>> Patch 1 is v2. In v1, I directly replaced writel with writel_relaxed in
>> queue_inc_prod. But Robin figured that it may lead SMMU consume stale
>> memory contents. I thought more than 3 whole days and got this one.
>>
>> This patchset is based on Robin Murphy's [PATCH v2 0/8] io-pgtable lock removal.
> 
> For the time being, I think we should focus on the new TLB flushing
> interface posted by Joerg:
> 
> http://lkml.kernel.org/r/1502974596-23835-1-git-send-email-joro@8bytes.org
> 
> which looks like it can give us most of the benefits of this series. Once
> we've got that, we can see what's left in the way of performance and focus
> on the cmdq batching separately (because I'm still not convinced about it).
OK, this is a good news.

But I have a review comment(sorry, I have not subscribed it yet, so can not directly reply it):
I don't think we should add tlb sync for map operation
1. at init time, all tlbs will be invalidated
2. when we try to map a new range, there are no related ptes bufferd in tlb, because of above 1 and below 3
3. when we unmap the above range, make sure all related ptes bufferd in tlb to be invalidated before unmap finished

> 
> Thanks,
> 
> Will
> 
> .
> 

-- 
Thanks!
BestRegards