linux-kernel - Re: [PATCH] iommu/arm-smmu-v3: add nr_ats_masters to avoid unnecessary operations

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Date:   Wed, 14 Aug 2019 08:41:37 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Will Deacon <will@...nel.org>, John Garry <john.garry@...wei.com>
CC:     Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        <jean-philippe@...aro.org>
Subject: Re: [PATCH] iommu/arm-smmu-v3: add nr_ats_masters to avoid
 unnecessary operations



On 2019/8/14 1:10, Will Deacon wrote:
> On Mon, Aug 12, 2019 at 11:42:17AM +0100, John Garry wrote:
>> On 01/08/2019 13:20, Zhen Lei wrote:
>>> When (smmu_domain->smmu->features & ARM_SMMU_FEAT_ATS) is true, even if a
>>> smmu domain does not contain any ats master, the operations of
>>> arm_smmu_atc_inv_to_cmd() and lock protection in arm_smmu_atc_inv_domain()
>>> are always executed. This will impact performance, especially in
>>> multi-core and stress scenarios. For my FIO test scenario, about 8%
>>> performance reduced.
>>>
>>> In fact, we can use a atomic member to record how many ats masters the
>>> smmu contains. And check that without traverse the list and check all
>>> masters one by one in the lock protection.
>>>
>>
>> Hi Will, Robin, Jean-Philippe,
>>
>> Can you kindly check this issue? We have seen a signifigant performance
>> regression here.
> 
> Sorry, John: Robin and Jean-Philippe are off at the moment and I've been
> swamped dealing with the arm64 queue. I'll try to get to this tomorrow.

Hi, all:
   I found my patch have some mistake, see below. I'm sorry I didn't see this coupling. 
I'm preparing v2. 

> @@ -1915,10 +1921,10 @@ static void arm_smmu_detach_dev(struct arm_smmu_master *master)
>  	list_del(&master->domain_head);
>  	spin_unlock_irqrestore(&smmu_domain->devices_lock, flags);
>  
> -	master->domain = NULL;
>  	arm_smmu_install_ste_for_dev(master);

"master->domain = NULL" is needed in arm_smmu_install_ste_for_dev().

>  
>  	arm_smmu_disable_ats(master);
> +	master->domain = NULL;
>  }

> 
> Will
> 
> .
>