linux-kernel - Re: [PATCH 4/7] node: Add memory caching attributes

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Message-ID: <731533d5-26e1-ade7-1a63-d1f85461d091@arm.com>
Date:   Thu, 22 Nov 2018 18:59:21 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Keith Busch <keith.busch@...el.com>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rafael Wysocki <rafael@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 4/7] node: Add memory caching attributes



On 11/20/2018 04:36 AM, Keith Busch wrote:
> On Mon, Nov 19, 2018 at 09:44:00AM +0530, Anshuman Khandual wrote:
>> On 11/15/2018 04:19 AM, Keith Busch wrote:
>>> System memory may have side caches to help improve access speed. While
>>> the system provided cache is transparent to the software accessing
>>> these memory ranges, applications can optimize their own access based
>>> on cache attributes.
>>
>> Cache is not a separate memory attribute. It impacts how the real attributes
>> like bandwidth, latency e.g which are already captured in the previous patch.
>> What is the purpose of adding this as a separate attribute ? Can you explain
>> how this is going to help the user space apart from the hints it has already
>> received with bandwidth, latency etc properties.
> 
> I am not sure I understand the question here. Access bandwidth and latency
> are entirely attributes different than what this patch provides. If the
> system side-caches memory, the associativity, line size, and total size
> can optionally be used by software to improve performance.

Okay but then does this belong to this series which about memory attributes ?