From: Dave Hansen <dave.hansen@intel.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
Keith Busch <keith.busch@intel.com>,
linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org,
linux-mm@kvack.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Rafael Wysocki <rafael@kernel.org>,
Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH 0/7] ACPI HMAT memory sysfs representation
Date: Mon, 26 Nov 2018 09:20:04 -0800 [thread overview]
Message-ID: <3b86c5c5-53f2-29bf-48e7-5749c7287dca@intel.com> (raw)
In-Reply-To: <1a9e887b-8087-e897-6195-e8df325bd458@arm.com>
On 11/26/18 7:38 AM, Anshuman Khandual wrote:
> On 11/24/2018 12:51 AM, Dave Hansen wrote:
>> On 11/22/18 10:42 PM, Anshuman Khandual wrote:
>>> Are we willing to go in the direction for inclusion of a new system
>>> call, subset of it appears on sysfs etc ? My primary concern is not
>>> how the attribute information appears on the sysfs but lack of it's
>>> completeness.
>>
>> A new system call makes total sense to me. I have the same concern
>> about the completeness of what's exposed in sysfs, I just don't see a
>> _route_ to completeness with sysfs itself. Thus, the minimalist
>> approach as a first step.
>
> Okay if we agree on the need for a new specific system call extracting
> the superset attribute information MAX_NUMNODES * MAX_NUMNODES * U64
> (u64 packs 8 bit values for 8 attributes or something like that) as we
> had discussed before, it makes sense to export a subset of it which can
> be faster but useful for the user space without going through a system
> call.
The information that needs to be exported is a bit more than that. It's
not just a binary attribute.
The information we have from the new ACPI table, for instance, is the
read and write bandwidth and latency between two nodes. They are, IIRC,
two-byte values in the ACPI table[1], each. That's 8 bytes worth of
data right there, which wouldn't fit *anything* else.
The list of things we want to export will certainly grow. That means we
need a syscall something like this:
int get_mem_attribute(unsigned long attribute_nr,
unsigned long __user * initiator_nmask,
unsigned long __user * target_nmask,
unsigned long maxnode,
unsigned long *attributes_out);
#define MEM_ATTR_READ_BANDWIDTH 1
#define MEM_ATTR_WRITE_BANDWIDTH 2
#define MEM_ATTR_READ_LATENCY 3
#define MEM_ATTR_WRITE_LATENCTY 4
#define MEM_ATTR_ENCRYPTION 5
If you want to know the read latency between nodes 4 and 8, you do:
ret = get_mem_attr(MEM_ATTR_READ_LATENCY,
(1<<4), (1<<8), max, &array);
And the answer shows up at array[0] in this example. If you had more
than one bit set in the two nmasks, you would have a longer array.
The length of the array is the number of bits set in initiator_nmask *
the number of bits set in target_nmask * sizeof(ulong).
This has the advantage of supporting ULONG_MAX attributes, and scales
from asking for one attribute at a time all the way up to dumping the
entire system worth of data for a single attribute. The only downside
is that it's one syscall per attribute instead of packing them all
together. But, if we have a small enough number to pack them in one
ulong, then I think we can make 64 syscalls without too much trouble.
> Do you agree on a (system call + sysfs) approach in principle ?
> Also sysfs exported information has to be derived from whats available
> through the system call not the other way round. Hence the starting
> point has to be the system call definition.
Both the sysfs information *and* what will be exported in any future
interfaces are derived from platform-specific information. They are not
derived from one _interface_ or the other.
They obviously need to be consistent, though.
1. See "Table 5-142 System Locality Latency and Bandwidth Information
Structure" here:
http://www.uefi.org/sites/default/files/resources/ACPI_6_2.pdf
next prev parent reply other threads:[~2018-11-26 17:20 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-14 22:49 [PATCH 0/7] ACPI HMAT memory sysfs representation Keith Busch
2018-11-16 6:27 ` Anshuman Khandual
2018-11-16 15:51 ` Keith Busch
2018-11-19 1:52 ` Anshuman Khandual
2018-11-16 16:55 ` Dave Hansen
2018-11-19 5:44 ` Anshuman Khandual
2018-11-19 17:37 ` Dave Hansen
2018-11-22 11:52 ` Anshuman Khandual
2018-11-22 18:01 ` Dave Hansen
2018-11-23 6:42 ` Anshuman Khandual
2018-11-23 19:21 ` Dave Hansen
2018-11-23 21:13 ` Dan Williams
2018-11-26 15:52 ` Anshuman Khandual
2018-11-26 16:42 ` Dave Hansen
2018-11-26 18:08 ` Dan Williams
2018-11-27 10:15 ` Anshuman Khandual
2018-11-27 16:56 ` Dan Williams
2018-11-26 15:38 ` Anshuman Khandual
2018-11-26 17:20 ` Dave Hansen [this message]
2018-11-27 9:32 ` Anshuman Khandual
2018-11-22 18:08 ` Dan Williams
2018-11-23 7:10 ` Anshuman Khandual
2018-11-23 17:15 ` Dan Williams
2018-11-27 14:05 ` Anshuman Khandual
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