linux-kernel - RE: [PATCH] iommu/vt-d: Link cache tags of same iommu unit together

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Message-ID: <SJ0PR11MB6744B797F0607503FC00E03192052@SJ0PR11MB6744.namprd11.prod.outlook.com>
Date: Wed, 18 Dec 2024 09:12:34 +0000
From: "Duan, Zhenzhong" <zhenzhong.duan@...el.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>
CC: "dwmw2@...radead.org" <dwmw2@...radead.org>, "joro@...tes.org"
	<joro@...tes.org>, "will@...nel.org" <will@...nel.org>,
	"robin.murphy@....com" <robin.murphy@....com>, "Liu, Yi L"
	<yi.l.liu@...el.com>, "Peng, Chao P" <chao.p.peng@...el.com>
Subject: RE: [PATCH] iommu/vt-d: Link cache tags of same iommu unit together



>-----Original Message-----
>From: Baolu Lu <baolu.lu@...ux.intel.com>
>Subject: Re: [PATCH] iommu/vt-d: Link cache tags of same iommu unit together
>
>On 2024/12/18 13:22, Duan, Zhenzhong wrote:
>>> -----Original Message-----
>>> From: Baolu Lu<baolu.lu@...ux.intel.com>
>>> Subject: Re: [PATCH] iommu/vt-d: Link cache tags of same iommu unit
>together
>>>
>>> On 12/16/24 11:38, Zhenzhong Duan wrote:
>>>> Cache tag invalidation requests for a domain are accumulated until a
>>>> different iommu unit is found when traversing the cache_tags linked list.
>>>> But cache tags of same iommu unit can be distributed in the linked list,
>>>> this make batched flush less efficient. E.g., one device backed by iommu0
>>>> is attached to a domain in between two devices attaching backed by iommu1.
>>>>
>>>> Group cache tags together for same iommu unit in cache_tag_assign() to
>>>> maximize the performance of batched flush.
>>>>
>>>> Signed-off-by: Zhenzhong Duan<zhenzhong.duan@...el.com>
>>>> ---
>>>>    drivers/iommu/intel/cache.c | 11 ++++++++++-
>>>>    1 file changed, 10 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/iommu/intel/cache.c b/drivers/iommu/intel/cache.c
>>>> index e5b89f728ad3..726052a841e0 100644
>>>> --- a/drivers/iommu/intel/cache.c
>>>> +++ b/drivers/iommu/intel/cache.c
>>>> @@ -48,6 +48,8 @@ static int cache_tag_assign(struct dmar_domain
>*domain,
>>> u16 did,
>>>>    	struct intel_iommu *iommu = info->iommu;
>>>>    	struct cache_tag *tag, *temp;
>>>>    	unsigned long flags;
>>>> +	struct cache_tag *temp2 = list_entry(&domain->cache_tags,
>>>> +					     struct cache_tag, node);
>>> Is this valid for a list head?
>> Yes, it's not valid for list head but it's intentional, just want to
>> avoid unnecessary temp2 check. If I don't do that way, patch will be:
>>
>> --- a/drivers/iommu/intel/cache.c
>> +++ b/drivers/iommu/intel/cache.c
>> @@ -48,6 +48,7 @@ static int cache_tag_assign(struct dmar_domain *domain,
>u16 did,
>>          struct intel_iommu *iommu = info->iommu;
>>          struct cache_tag *tag, *temp;
>>          unsigned long flags;
>> +       struct cache_tag *temp2 = NULL;
>>
>>          tag = kzalloc(sizeof(*tag), GFP_KERNEL);
>>          if (!tag)
>> @@ -73,8 +74,18 @@ static int cache_tag_assign(struct dmar_domain
>*domain, u16 did,
>>                          trace_cache_tag_assign(temp);
>>                          return 0;
>>                  }
>> +               if (temp->iommu == iommu)
>> +                       temp2 = temp;
>>          }
>> -       list_add_tail(&tag->node, &domain->cache_tags);
>> +       /*
>> +        * Link cache tags of same iommu unit together, so consponding
>> +        * flush ops can be batched for iommu unit.
>> +        */
>> +       if (temp2)
>> +               list_add(&tag->node, &temp2->node);
>> +       else
>> +               list_add_tail((&tag->node, &domain->cache_tags);
>> +
>>          spin_unlock_irqrestore(&domain->cache_lock, flags);
>>          trace_cache_tag_assign(tag);
>
>Perhaps we can make it like this?

Good suggestion! Will do.

Thanks
Zhenzhong

>
>diff --git a/drivers/iommu/intel/cache.c b/drivers/iommu/intel/cache.c
>index 09694cca8752..cf0cca94d165 100644
>--- a/drivers/iommu/intel/cache.c
>+++ b/drivers/iommu/intel/cache.c
>@@ -47,6 +47,7 @@ static int cache_tag_assign(struct dmar_domain
>*domain, u16 did,
>         struct device_domain_info *info = dev_iommu_priv_get(dev);
>         struct intel_iommu *iommu = info->iommu;
>         struct cache_tag *tag, *temp;
>+       struct list_head *prev;
>         unsigned long flags;
>
>         tag = kzalloc(sizeof(*tag), GFP_KERNEL);
>@@ -65,6 +66,7 @@ static int cache_tag_assign(struct dmar_domain
>*domain, u16 did,
>                 tag->dev = iommu->iommu.dev;
>
>         spin_lock_irqsave(&domain->cache_lock, flags);
>+       prev = &domain->cache_tags;
>         list_for_each_entry(temp, &domain->cache_tags, node) {
>                 if (cache_tage_match(temp, did, iommu, dev, pasid, type)) {
>                         temp->users++;
>@@ -73,8 +75,15 @@ static int cache_tag_assign(struct dmar_domain
>*domain, u16 did,
>                         trace_cache_tag_assign(temp);
>                         return 0;
>                 }
>+               if (temp->iommu == iommu)
>+                       prev = &temp->node;
>         }
>-       list_add_tail(&tag->node, &domain->cache_tags);
>+       /*
>+        * Link cache tags of same iommu unit together, so consponding
>+        * flush ops can be batched for iommu unit.
>+        */
>+       list_add(&tag->node, prev);
>+
>         spin_unlock_irqrestore(&domain->cache_lock, flags);
>         trace_cache_tag_assign(tag);
>
>Thanks,
>baolu