linux-kernel - Re: [PATCH 3/3] iommu/vt-d: Size Page Request Queue to avoid overflow condition

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Date:   Mon, 18 Apr 2022 19:44:44 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     baolu.lu@...ux.intel.com,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] iommu/vt-d: Size Page Request Queue to avoid overflow
 condition

On 2022/4/18 15:00, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@...ux.intel.com>
>> Sent: Saturday, April 16, 2022 8:31 PM
>>
>> PRQ overflow may cause I/O throughput congestion, resulting in unnecessary
>> degradation of IO performance. Appropriately increasing the length of PRQ
>> can greatly reduce the occurrence of PRQ overflow. The count of maximum
>> page requests that can be generated in parallel by a PCIe device is
>> statically defined in the Outstanding Page Request Capacity field of the
>> PCIe ATS configure space.
>>
>> The new lenght of PRQ is calculated by summing up the value of Outstanding
>> Page Request Capacity register across all devices where Page Requests are
>> supported on the real PR-capable platfrom (Intel Sapphire Rapids). The
>> result is round to the nearest higher power of 2.
> The actual requirement is usage and platform specific. What about
> doubling the default size and also provide an option for admin to
> tune?

I also have this in my list to provide an opt-in interface for user. But
I don't want to include it in this series as this is only for small
tuning. The opt-in interface looks more like a new feature. :-)

Best regards,
baolu