On Thu, May 03, 2012 at 10:38:56AM +0200, Sasha Levin wrote: > On Thu, May 3, 2012 at 9:32 AM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Thu, May 03, 2012 at 07:51:18AM +0200, Sasha Levin wrote: > >> On Thu, May 3, 2012 at 7:29 AM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > >> > Sasha, didn't you have a patch to allocate > >> > things using cache in virtio core? > >> > What happened to it? > >> > > >> > Thanks, > >> > MST > >> > >> It got stuck due to several things, and I got sidetracked, sorry. Here > >> are the outstanding issues: > >> > >> 1. Since now we can allocate a descriptor either using kmalloc or from > >> the cache, we need a new flag in vring_desc to know how to free it, it > >> seems a bit too intrusive, > >> and I couldn't thing of a better > >> alternative. > > > > Since that is guest visible it does not sound great, I agree. > > > > Three ideas: > > 1. The logic looks at descriptor size so can we just read > > desc.len before free and rerun the same math? > > It'll break every time the value is changed (either by the user or by > some dynamic algorithm thingie). Yes but did you intend to implement such complex logic? If not let's not over-engineer. > > 2. For -net the requests are up to max_skb_frags + 2 in size, right? > > Does it make sense to just use cache for net, always? > > That would mean a per device flag. > > Yup, it could work. > > > 3. Allocate a bit more and stick extra data before the 1st descriptor. > > I guess it'll work, but it just seems a bit ugly :) An understatement. > >> 2. Rusty has pointed out that no one is going to modify the default > >> value we set, and we don't really have a good default value to put > >> there (at least, we haven't agreed on a specific value). Also, you > >> have noted that it should be a per-device value, which complicates > >> this question further since we probably want a different value for > >> each device type. > >> > >> While the first one can be solved easily with a blessing from the > >> maintainers, the second one will require testing on various platforms, > >> configurations and devices to select either the best "magic" value, or > >> the best algorithm to play with threshold. > > > > Not sure about platforms but for devices that's right. > > But this really only means we only change what we tested. > > eg see what is good for net and change net in a way > > that others will keep using old code. > > It'll work only if there will be someone following up and actually > testing it, since regular users won't be testing it at all (with it > being defaulted to off and everything). Not sure I understand. Whatever patch gets applied will be tested beforehand. -- 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
