On Mon, Sep 02, 2019 at 09:39:12AM +0100, Stefan Hajnoczi wrote:

On Sun, Sep 01, 2019 at 02:56:44AM -0400, Michael S. Tsirkin wrote:

quoted

OK let me try to clarify.  The idea is this:

Let's say we queue a buffer of 4K, and we copy if len < 128 bytes.  This
means that in the worst case (128 byte packets), each byte of credit in
the socket uses up 4K/128 = 16 bytes of kernel memory. In fact we need
to also account for the virtio_vsock_pkt since I think it's kept around
until userspace consumes it.

Thus given X buf alloc allowed in the socket, we should publish X/16
credits to the other side. This will ensure the other side does not send
more than X/16 bytes for a given socket and thus we won't need to
allocate more than X bytes to hold the data.

We can play with the copy break value to tweak this.

Thanks Michael, now it is perfectly clear. It seems an excellent solution and
easy to implement. I'll work on that.

This seems like a reasonable solution.  Hopefully the benchmark results
will come out okay too.

Yes, as Michael suggested I'll play with the copy break value to see as
benchmark has affected.

Thank you very much,
Stefano