On Tue, May 17, 2011 at 03:28:38PM -0700, Shirley Ma wrote: > On Tue, 2011-05-17 at 23:48 +0200, MichaÅ MirosÅaw wrote: > > 2011/5/17 Shirley Ma <mashirle@xxxxxxxxxx>: > > > Hello Michael, > > > > > > Looks like to use a new flag requires more time/work. I am thinking > > > whether we can just use HIGHDMA flag to enable zero-copy in macvtap > > to > > > avoid the new flag for now since mavctap uses real NICs as lower > > device? > > > > Is there any other restriction besides requiring driver to not recycle > > the skb? Are there any drivers that recycle TX skbs? Not just recycling skbs, keeping reference to any of the pages in the skb. Another requirement is to invoke the callback in a timely fashion. For example virtio-net doesn't limit the time until that happens (skbs are only freed when some other packet is transmitted), so we need to avoid zcopy for such (nested-virt) scenarious, right? > > Not more other restrictions, skb clone is OK. pskb_expand_head() looks > OK to me from code review. Hmm. pskb_expand_head calls skb_release_data while keeping references to pages. How is that ok? What do I miss? > Currently there is no drivers recycle TX skbs. > > Thanks > Shirley Well, with e.g. bridge or veth the skb might enter the host networking stack. Once that happens, we lose track of the pages. Or is there anything that prevents such setups? -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
