Messages in this thread | | | Date | Wed, 15 Jan 2014 13:33:52 -0800 | Subject | Re: [PATCH v3 1/4] net_dma: simple removal | From | Dan Williams <> |
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On Wed, Jan 15, 2014 at 1:31 PM, Dan Williams <dan.j.williams@intel.com> wrote: > On Wed, Jan 15, 2014 at 1:20 PM, saeed bishara <saeed.bishara@gmail.com> wrote: >> Hi Dan, >> >> I'm using net_dma on my system and I achieve meaningful performance >> boost when running Iperf receive. >> >> As far as I know the net_dma is used by many embedded systems out >> there and might effect their performance. >> Can you please elaborate on the exact scenario that cause the memory corruption? >> >> Is the scenario mentioned here caused by "real life" application or >> this is more of theoretical issue found through manual testing, I was >> trying to find the thread describing the failing scenario and couldn't >> find it, any pointer will be appreciated. > > Did you see the referenced commit? > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=77873803363c > > This is a real issue in that any app that forks() while receiving data > can cause the dma data to be lost. The problem is that the copy > operation falls back to cpu at many locations. Any one of those > instance could touch a mapped page and trigger a copy-on-write event. > The dma completes to the wrong location. >
Btw, do you have benchmark data showing that NET_DMA is beneficial on these platforms? I would have expected worse performance on platforms without i/o coherent caches.
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