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From: "Mattias Rönnblom" <hofors@lysator.liu.se>
To: "Morten Brørup" <mb@smartsharesystems.com>,
	dev@dpdk.org, "Bruce Richardson" <bruce.richardson@intel.com>,
	"Konstantin Ananyev" <konstantin.v.ananyev@yandex.ru>
Cc: Jan Viktorin <viktorin@rehivetech.com>,
	Ruifeng Wang <ruifeng.wang@arm.com>,
	David Christensen <drc@linux.vnet.ibm.com>,
	Stanislaw Kardach <kda@semihalf.com>
Subject: Re: [RFC v2] non-temporal memcpy
Date: Tue, 9 Aug 2022 14:05:12 +0200	[thread overview]
Message-ID: <44172db2-5f03-e58e-f72c-76eac1cd192c@lysator.liu.se> (raw)
In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35D87247@smartserver.smartshare.dk>

On 2022-08-09 11:46, Morten Brørup wrote:
>> From: Mattias Rönnblom [mailto:hofors@lysator.liu.se]
>> Sent: Sunday, 7 August 2022 22.25
>>
>> On 2022-07-19 17:26, Morten Brørup wrote:
>>> This RFC proposes a set of functions optimized for non-temporal
>> memory copy.
>>>
>>> At this stage, I am asking for feedback on the concept.
>>>
>>> Applications sometimes data to another memory location, which is only
>> used
>>> much later.
>>> In this case, it is inefficient to pollute the data cache with the
>> copied
>>> data.
>>>
>>> An example use case (originating from a real life application):
>>> Copying filtered packets, or the first part of them, into a capture
>> buffer
>>> for offline analysis.
>>>
>>> The purpose of these functions is to achieve a performance gain by
>> not
>>> polluting the cache when copying data.
>>> Although the throughput may be improved by further optimization, I do
>> not
>>> consider througput optimization relevant initially.
>>>
>>> The x86 non-temporal load instructions have 16 byte alignment
>>> requirements [1], while ARM non-temporal load instructions are
>> available with
>>> 4 byte alignment requirements [2].
>>> Both platforms offer non-temporal store instructions with 4 byte
>> alignment
>>> requirements.
>>>
>>
>> I don't think memcpy() functions should have alignment requirements.
>> That's not very practical, and violates the principle of least
>> surprise.
> 
> I didn't make the CPUs with these alignment requirements.
> 
> However, I will offer optimized performance in a generic NT memcpy() function in the cases where the individual alignment requirements of various CPUs happen to be met.
> 
>>
>> Use normal memcpy() for the unaligned parts, and for the whole thing
>> for
>> small sizes (at least on x86).
>>
> 
> I'm not going to plunge into some advanced vector programming, so I'm working on an implementation where misalignment is handled by using a bounce buffer (allocated on the stack, which is probably cache hot anyway).
> 
> 

I don't know for the NT load + NT store case, but for regular load + NT 
store, this is trivial. The implementation I've used is 36 
straight-forward lines of code.

  reply	other threads:[~2022-08-09 12:05 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-07-19 15:26 Morten Brørup
2022-07-19 18:00 ` David Christensen
2022-07-19 18:41   ` Morten Brørup
2022-07-19 18:51     ` Stanisław Kardach
2022-07-19 22:15       ` Morten Brørup
2022-07-21 23:19 ` Konstantin Ananyev
2022-07-22 10:44   ` Morten Brørup
2022-07-24 13:35     ` Konstantin Ananyev
2022-07-24 22:18       ` Morten Brørup
2022-07-29 10:00         ` Konstantin Ananyev
2022-07-29 10:46           ` Morten Brørup
2022-07-29 11:50             ` Konstantin Ananyev
2022-07-29 17:17               ` Morten Brørup
2022-07-29 22:00                 ` Konstantin Ananyev
2022-07-30  9:51                   ` Morten Brørup
2022-08-02  9:05                     ` Konstantin Ananyev
2022-07-29 12:13             ` Konstantin Ananyev
2022-07-29 16:05               ` Stephen Hemminger
2022-07-29 17:29                 ` Morten Brørup
2022-08-07 20:40                 ` Mattias Rönnblom
2022-08-09  9:24                   ` Morten Brørup
2022-08-09 11:53                     ` Mattias Rönnblom
2022-10-09 16:16                       ` Morten Brørup
2022-07-29 18:13               ` Morten Brørup
2022-07-29 19:49                 ` Konstantin Ananyev
2022-07-29 20:26                   ` Morten Brørup
2022-07-29 21:34                     ` Konstantin Ananyev
2022-08-07 20:20                     ` Mattias Rönnblom
2022-08-09  9:34                       ` Morten Brørup
2022-08-09 11:56                         ` Mattias Rönnblom
2022-08-10 21:05                     ` Honnappa Nagarahalli
2022-08-11 11:50                       ` Mattias Rönnblom
2022-08-11 16:26                         ` Honnappa Nagarahalli
2022-07-25  1:17       ` Honnappa Nagarahalli
2022-07-27 10:26         ` Morten Brørup
2022-07-27 17:37           ` Honnappa Nagarahalli
2022-07-27 18:49             ` Morten Brørup
2022-07-27 19:12               ` Stephen Hemminger
2022-07-28  9:00                 ` Morten Brørup
2022-07-27 19:52               ` Honnappa Nagarahalli
2022-07-27 22:02                 ` Stanisław Kardach
2022-07-28 10:51                   ` Morten Brørup
2022-07-29  9:21                     ` Konstantin Ananyev
2022-08-07 20:25 ` Mattias Rönnblom
2022-08-09  9:46   ` Morten Brørup
2022-08-09 12:05     ` Mattias Rönnblom [this message]
2022-08-09 15:00       ` Morten Brørup
2022-08-10 11:47         ` Mattias Rönnblom
2022-08-09 15:26     ` Stephen Hemminger
2022-08-09 17:24       ` Morten Brørup
2022-08-10 11:59         ` Mattias Rönnblom
2022-08-10 12:12           ` Morten Brørup
2022-08-10 11:55       ` Mattias Rönnblom
2022-08-10 12:18         ` Morten Brørup
2022-08-10 21:20           ` Honnappa Nagarahalli
2022-08-11 11:53             ` Mattias Rönnblom
2022-08-11 22:24               ` Honnappa Nagarahalli

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