From: Jason Gunthorpe <jgg@ziepe.ca>
To: "hch@lst.de" <hch@lst.de>
Cc: Thomas Hellstrom <thellstrom@vmware.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"yong.zhi@intel.com" <yong.zhi@intel.com>,
"daniel.vetter@ffwll.ch" <daniel.vetter@ffwll.ch>,
"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
"syeh@vmware.com" <syeh@vmware.com>,
"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
"bingbu.cao@intel.com" <bingbu.cao@intel.com>,
"imre.deak@intel.com" <imre.deak@intel.com>,
"tian.shu.qiu@intel.com" <tian.shu.qiu@intel.com>,
"jian.xu.zheng@intel.com" <jian.xu.zheng@intel.com>,
"shiraz.saleem@intel.com" <shiraz.saleem@intel.com>,
"sakari.ailus@linux.intel.com" <sakari.ailus@linux.intel.com>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH] lib/scatterlist: Provide a DMA page iterator
Date: Thu, 17 Jan 2019 08:54:17 -0700 [thread overview]
Message-ID: <20190117155417.GA9629@ziepe.ca> (raw)
In-Reply-To: <20190117093001.GB31303@lst.de>
On Thu, Jan 17, 2019 at 10:30:01AM +0100, hch@lst.de wrote:
> On Wed, Jan 16, 2019 at 10:24:36AM -0700, Jason Gunthorpe wrote:
> > The fact is there is 0 industry interest in using RDMA on platforms
> > that can't do HW DMA cache coherency - the kernel syscalls required to
> > do the cache flushing on the IO path would just destroy performance to
> > the point of making RDMA pointless. Better to use netdev on those
> > platforms.
>
> In general there is no syscall required for doing cache flushing, you
> just issue the proper instructions directly from userspace.
At least on the ARM/MIPS systems I've worked with like this the cache
manipulation instructions are privileged and cannot be executed by
userspace. So the general case requires a syscall.
> In that case we just need to block userspace DMA access entirely.
> Which given the amount of problems it creates sounds like a pretty
> good idea anyway.
I doubt there is any support for that idea...
Jason
next prev parent reply other threads:[~2019-01-17 15:54 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-04 22:35 [PATCH] lib/scatterlist: Provide a DMA page iterator Jason Gunthorpe
2019-01-05 2:37 ` kbuild test robot
2019-01-05 3:21 ` Jason Gunthorpe
2019-01-10 23:42 ` Jason Gunthorpe
2019-01-14 9:48 ` Christoph Hellwig
2019-01-15 14:17 ` Thomas Hellstrom
2019-01-15 14:24 ` Christian König
2019-01-15 15:20 ` hch
2019-01-15 18:03 ` Thomas Hellstrom
2019-01-15 18:31 ` hch
2019-01-15 19:13 ` Koenig, Christian
2019-01-15 20:58 ` hch
2019-01-16 7:09 ` Thomas Hellstrom
2019-01-16 7:28 ` Koenig, Christian
2019-01-16 10:14 ` Daniel Vetter
2019-01-16 16:06 ` hch
2019-01-16 16:36 ` Daniel Stone
2019-01-15 21:25 ` Jason Gunthorpe
2019-01-16 10:40 ` Christian König
2019-01-16 16:11 ` hch
2019-01-16 17:24 ` Jason Gunthorpe
2019-01-17 9:30 ` hch
2019-01-17 10:47 ` Thomas Hellstrom
2019-01-17 15:54 ` Jason Gunthorpe [this message]
2019-01-12 18:27 ` Shiraz Saleem
2019-01-12 18:37 ` Jason Gunthorpe
2019-01-12 19:03 ` Shiraz Saleem
2019-01-14 9:46 ` Christoph Hellwig
2019-01-14 22:16 ` Jason Gunthorpe
2019-02-07 23:23 ` Sakari Ailus
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