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From: "Morten Brørup" <mb@smartsharesystems.com>
To: "Mattias Rönnblom" <hofors@lysator.liu.se>,
	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 17:00:37 +0200	[thread overview]
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35D8724B@smartserver.smartshare.dk> (raw)
In-Reply-To: <44172db2-5f03-e58e-f72c-76eac1cd192c@lysator.liu.se>

> From: Mattias Rönnblom [mailto:hofors@lysator.liu.se]
> Sent: Tuesday, 9 August 2022 14.05
> 
> 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.

Is that implementation available for inspiration anywhere?


  reply	other threads:[~2022-08-09 15:00 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
2022-08-09 15:00       ` Morten Brørup [this message]
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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