On Wed 05 Jun 00:33 PDT 2019, Arnaud Pouliquen wrote: > 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. > Having an implementation that uses small fixed size buffers seems very reasonable and I'm in favour of making the message size configurable. I would however prefer to have this implemented in a way where the remote side should not be receiving messages in a way that's based on the remote side's allocation parameters. I don't think this series prevents the introduction of such isolation, but it would render this code unnecessary. Regards, Bjorn
