Hi Ohad, On Thu, Feb 21, 2013 at 6:55 PM, Ohad Ben-Cohen <o...@wizery.com> wrote: > On Thu, Feb 21, 2013 at 7:28 PM, Sjur Brændeland <sjurb...@gmail.com> wrote: >> The motivation for using vringh was to avoid copying buffers >> when sending data from the modem to the host. > > I may be missing something here, but why do you need vringh for that? > > With rpmsg (which uses two regular vrings) both ends send huge amount > of data without copying it - we just send the pointers across.
OK, We did carefully consider using the normal vrings, but concluded it was not doable. I'll try to give you some of the background that I can recall from top of my head. (I can dig out more if you're still not convinced :) The modem we're integrating with is a complex beast (multi mode modem LTE, HSPA+, etc). When a packet is received deep down in the radio stack, it allocates packet buffers using the internal slab allocator.The packet may contain anything from control, voice, or IP packets. If the packet contains IP-payload it will travel to a different asymmetric CPU that handles the IPC towards the modem. If the packet is not a IP-packet it will be processed internally and eventually freed. What we have done to integrate virtio is to inject the carveout into the the modem internal slab-allocator. Using the reversed ring allows us to introduce zero-copy for virtio with virtually no impact on the radio-stack, only a small change on the modem slab allocator. It supports dynamic size buffer allocation, and modem internal messaging using data allocated from the shared region. It also allows modem to manage it's own memory, without any dependency on host side allocators. Thanks, Sjur -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
