LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: iommu@lists.linux-foundation.org,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	"Tariq Toukan" <tariqt@mellanox.com>,
	"Ilias Apalodimas" <ilias.apalodimas@linaro.org>,
	"Toke Høiland-Jørgensen" <toke@toke.dk>,
	"Robin Murphy" <robin.murphy@arm.com>,
	linux-kernel@vger.kernel.org, brouer@redhat.com
Subject: Re: [RFC] avoid indirect calls for DMA direct mappings
Date: Thu, 6 Dec 2018 18:43:51 +0100
Message-ID: <20181206184351.4d9ece54@redhat.com> (raw)
In-Reply-To: <20181206153720.10702-1-hch@lst.de>

On Thu,  6 Dec 2018 07:37:19 -0800
Christoph Hellwig <hch@lst.de> wrote:

> Hi all,
> 
> a while ago Jesper reported major performance regressions due to the
> spectre v2 mitigations in his XDP forwarding workloads.  A large part
> of that is due to the DMA mapping API indirect calls.
> 
> It turns out that the most common implementation of the DMA API is the
> direct mapping case, and now that we have merged almost all duplicate
> implementations of that into a single generic one is easily feasily to
> direct calls for this fast path.
> 
> This patch adds a check if we are using dma_direct_ops in each fast path
> DMA operation, and just uses a direct call instead.  For the XDP workload
> this increases the number of packets per second from 7,438,283 to
> 9,610,088, so it provides a very significant speedup.

Full test report avail here:
 https://github.com/xdp-project/xdp-project/blob/master/areas/dma/dma01_test_hellwig_direct_dma.org


> Note that the patch depends on a lot of work either queued up in the
> DMA mapping tree, or still out on the list from review, so to actually
> try the patch you probably want this git tree:
> 
> 
>     git://git.infradead.org/users/hch/misc.git dma-direct-calls
> 
> Gitweb:
> 
>     http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dma-direct-calls
> 



-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

  parent reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-06 15:37 Christoph Hellwig
2018-12-06 15:37 ` [PATCH] dma-mapping: bypass indirect calls for dma-direct Christoph Hellwig
2018-12-06 17:40   ` Jesper Dangaard Brouer
2018-12-06 18:35     ` Christoph Hellwig
2018-12-06 17:43 ` Jesper Dangaard Brouer [this message]
2018-12-06 18:29   ` [RFC] avoid indirect calls for DMA direct mappings Nadav Amit
2018-12-06 18:45     ` Christoph Hellwig
2018-12-06 18:28 ` Linus Torvalds
2018-12-06 18:30   ` Linus Torvalds
2018-12-06 18:43   ` Christoph Hellwig
2018-12-06 18:51     ` Linus Torvalds
2018-12-06 18:54     ` Robin Murphy
2018-12-06 20:00       ` Christoph Hellwig
2018-12-06 20:24         ` Robin Murphy
2018-12-07  1:21           ` Christoph Hellwig
2018-12-07 15:44             ` Jesper Dangaard Brouer
2018-12-07 16:05               ` Jesper Dangaard Brouer

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20181206184351.4d9ece54@redhat.com \
    --to=brouer@redhat.com \
    --cc=hch@lst.de \
    --cc=ilias.apalodimas@linaro.org \
    --cc=iommu@lists.linux-foundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=robin.murphy@arm.com \
    --cc=tariqt@mellanox.com \
    --cc=toke@toke.dk \
    --cc=torvalds@linux-foundation.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git