From: Christoph Hellwig <hch@lst.de>
To: Tushar Dave <tushar.n.dave@oracle.com>
Cc: "Christoph Hellwig" <hch@lst.de>,
"Jesper Dangaard Brouer" <brouer@redhat.com>,
"xdp-newbies@vger.kernel.org" <xdp-newbies@vger.kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"David Woodhouse" <dwmw2@infradead.org>,
"William Tu" <u9012063@gmail.com>,
"Björn Töpel" <bjorn.topel@intel.com>,
"Karlsson, Magnus" <magnus.karlsson@intel.com>,
"Alexander Duyck" <alexander.duyck@gmail.com>,
"Arnaldo Carvalho de Melo" <acme@redhat.com>
Subject: Re: XDP performance regression due to CONFIG_RETPOLINE Spectre V2
Date: Fri, 13 Apr 2018 19:26:11 +0200 [thread overview]
Message-ID: <20180413172611.GA23634@lst.de> (raw)
In-Reply-To: <fbcb4cc8-53fb-82cd-bd9d-76c5fdd47918@oracle.com>
On Fri, Apr 13, 2018 at 10:12:41AM -0700, Tushar Dave wrote:
> I guess there is nothing we need to do!
>
> On x86, in case of no intel iommu or iommu is disabled, you end up in
> swiotlb for DMA API calls when system has 4G memory.
> However, AFAICT, for 64bit DMA capable devices swiotlb DMA APIs do not
> use bounce buffer until and unless you have swiotlb=force specified in
> kernel commandline.
Sure. But that means very sync_*_to_device and sync_*_to_cpu now
involves an indirect call to do exactly nothing, which in the workload
Jesper is looking at is causing a huge performance degradation due to
retpolines.
next prev parent reply other threads:[~2018-04-13 17:26 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-12 13:50 XDP performance regression due to CONFIG_RETPOLINE Spectre V2 Jesper Dangaard Brouer
2018-04-12 14:51 ` Christoph Hellwig
2018-04-12 14:56 ` Christoph Hellwig
2018-04-12 15:31 ` Jesper Dangaard Brouer
2018-04-13 16:49 ` Christoph Hellwig
2018-04-13 17:12 ` Tushar Dave
2018-04-13 17:26 ` Christoph Hellwig [this message]
2018-04-14 19:29 ` David Woodhouse
2018-04-16 6:02 ` Jesper Dangaard Brouer
2018-04-16 12:27 ` Christoph Hellwig
2018-04-16 12:27 ` Christoph Hellwig
2018-04-16 16:04 ` Alexander Duyck
2018-04-17 6:19 ` Christoph Hellwig
2018-04-16 18:05 ` dma-mapping: bypass dma_ops for direct mappings kbuild test robot
2018-04-16 18:26 ` Jesper Dangaard Brouer
2018-04-16 18:31 ` kbuild test robot
2018-04-16 21:07 ` XDP performance regression due to CONFIG_RETPOLINE Spectre V2 Jesper Dangaard Brouer
2018-04-17 6:15 ` Christoph Hellwig
2018-04-17 7:07 ` Jesper Dangaard Brouer
2018-04-17 7:13 ` Christoph Hellwig
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