W dniu 18 maja 2011 01:44 użytkownik Shirley Ma <mashirle@xxxxxxxxxx> napisał: > On Wed, 2011-05-18 at 00:58 +0200, Michał Mirosław wrote: >> W dniu 18 maja 2011 00:28 użytkownik Shirley Ma <mashirle@xxxxxxxxxx> >> napisał: >> > On Tue, 2011-05-17 at 23:48 +0200, Michał Mirosław wrote: >> >> 2011/5/17 Shirley Ma <mashirle@xxxxxxxxxx>: >> >> > 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 more other restrictions, skb clone is OK. pskb_expand_head() >> looks >> > OK to me from code review. >> >> > Currently there is no drivers recycle TX skbs. >> >> So why do you require the target device to have some flags at all? > We could use macvtap to check lower device HIGHDMA to enable zero-copy, > but I am not sure whether it is sufficient. If it's sufficient then we > don't need to use a new flag here. To be safe, it's better to use a new > flag to enable each device who can pass zero-copy test. >> Do I understand correctly, that this zero-copy feature is about >> packets received from VMs? > Yes, packets sent from VMs, and received in local host for TX zero-copy > here. What is the zero-copy test? On some arches the HIGHDMA is not needed at all so might be not enabled on anything. It looks like the correct test would be per-packet check of !illegal_highdma() or maybe NETIF_F_SG as returned from harmonize_features(). For virtual devices or other software forwarding this might lead to skb_linearize() in some cases, but is it that bad? Best Regards, Michał Mirosław -- 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
