Hi Bjorn, On 6/5/19 6:34 AM, Bjorn Andersson wrote: > On Thu 31 Jan 07:41 PST 2019, Xiang Xiao wrote: > >> Hi, >> This series enhance the buffer allocation by: >> 1.Support the different buffer number in rx/tx direction >> 2.Get the individual rx/tx buffer size from config space >> >> Here is the related OpenAMP change: >> https://github.com/OpenAMP/open-amp/pull/155 >> > > This looks pretty reasonable, but can you confirm that it's possible to > use new firmware with an old Linux kernel when introducing this? > > > But ever since we discussed Loic's similar proposal earlier I've been > questioning if the fixed buffer size isn't just an artifact of how we > preallocate our buffers. The virtqueue seems to support arbitrary sizes > of buffers and I see that the receive function in OpenAMP has been fixed > to put back the buffer of the size that was received, rather than 512 > bytes. So it seems like Linux would be able to send whatever size > messages to OpenAMP it would handle it. > > The question is if we could do the same in the other direction, perhaps > by letting the OpenAMP side do it's message allocation when it's > sending, rather than Linux pushing inbufs to be filled by the remote. IMHO, both could be useful and could be not correlated. On-the fly buffer allocation seems more efficient but needs an allocator.This can be a generic allocator (with a va to da) for system where large amount of memories are accessible from both side. Now what about system with small shared memory? In this case you have to deal with a limited/optimized memory chunk. To avoid memory fragmentation the allocator should have a pre-reserved buffers pool(so similar to existing implementation). This serie seems useful to optimize the size of the pre-reserved pool. > > This would remove the problem of always having suboptimal buffer sizes. > > Regards, > Bjorn > >> Xiang Xiao (3): >> rpmsg: virtio_rpmsg_bus: allow the different vring size for send/recv >> rpmsg: virtio_rpmsg_bus: allocate rx/tx buffer separately >> rpmsg: virtio_rpmsg_bus: get buffer size from config space >> >> drivers/rpmsg/virtio_rpmsg_bus.c | 127 +++++++++++++++++++++++--------------- >> include/uapi/linux/virtio_rpmsg.h | 24 +++++++ >> 2 files changed, 100 insertions(+), 51 deletions(-) >> create mode 100644 include/uapi/linux/virtio_rpmsg.h >> >> -- >> 2.7.4 >> -- Regards, Arnaud
