From mboxrd@z Thu Jan  1 00:00:00 1970
From: jean-philippe.brucker@arm.com (Jean-Philippe Brucker)
Date: Mon, 3 Apr 2017 11:14:17 +0100
Subject: [RFC PATCH 04/30] iommu/arm-smmu-v3: Add support for PCI ATS
In-Reply-To: <CA+sq2CeWpGarhT9p+iVo8nJXR=xpkj6XNMwv4LvbP0M6JxA_SA@mail.gmail.com>
References: <20170227195441.5170-1-jean-philippe.brucker@arm.com>
 <20170227195441.5170-5-jean-philippe.brucker@arm.com>
 <CA+sq2CeWpGarhT9p+iVo8nJXR=xpkj6XNMwv4LvbP0M6JxA_SA@mail.gmail.com>
Message-ID: <5af054c8-28cd-6719-b506-d0133c03042b@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 03/04/17 09:34, Sunil Kovvuri wrote:
>> +static size_t arm_smmu_atc_invalidate_domain(struct arm_smmu_domain *smmu_domain,
>> +                                            unsigned long iova, size_t size)
>> +{
>> +       unsigned long flags;
>> +       struct arm_smmu_cmdq_ent cmd = {0};
>> +       struct arm_smmu_group *smmu_group;
>> +       struct arm_smmu_master_data *master;
>> +       struct arm_smmu_device *smmu = smmu_domain->smmu;
>> +       struct arm_smmu_cmdq_ent sync_cmd = {
>> +               .opcode = CMDQ_OP_CMD_SYNC,
>> +       };
>> +
>> +       spin_lock_irqsave(&smmu_domain->groups_lock, flags);
>> +
>> +       list_for_each_entry(smmu_group, &smmu_domain->groups, domain_head) {
>> +               if (!smmu_group->ats_enabled)
>> +                       continue;
> 
> If ATS is not supported, this seems to increase no of cycles spent in
> pgtbl_lock.
> Can we return from this API by checking 'ARM_SMMU_FEAT_ATS' in smmu->features ?

Sure, I can add a check before taking the lock. Have you been able to
observe a significant difference in cycles between checking FEAT_ATS,
checking group->ats_enabled after taking the lock, and removing this
function call altogether?

Thanks,
Jean-Philippe