On Wed, Oct 10, 2018 at 10:36:26AM -0400, Michael S. Tsirkin wrote: > On Thu, Sep 13, 2018 at 05:47:29PM +0800, Jason Wang wrote: > > On 2018年09月13日 16:59, Tiwei Bie wrote: > > > > If what you say is true then we should take a careful look > > > > and not supporting these generic things with packed layout. > > > > Once we do support them it will be too late and we won't > > > > be able to get performance back. > > > I think it's a good point that we don't need to support > > > everything in packed ring (especially these which would > > > hurt the performance), as the packed ring aims at high > > > performance. I'm also wondering about the features. Is > > > there any possibility that we won't support the out of > > > order processing (at least not by default) in packed ring? > > > If I didn't miss anything, the need to support out of order > > > processing in packed ring will make the data structure > > > inside the driver not cache friendly which is similar to > > > the case of the descriptor table in the split ring (the > > > difference is that, it only happens in driver now). > > > > Out of order is not the only user, DMA is another one. We don't have used > > ring(len), so we need to maintain buffer length somewhere even for in order > > device. > > For a bunch of systems dma unmap is a nop so we do not really > need to maintain it. It's a question of an API to detect that > and optimize for it. I posted a proposed patch for that - > want to try using that? Yeah, definitely! > > > But if it's not too late, I second for a OUT_OF_ORDER feature. > > Starting from in order can have much simpler code in driver. > > > > Thanks > > It's tricky to change the flag polarity because of compatibility > with legacy interfaces. Why is this such a big deal? > > Let's teach drivers about IN_ORDER, then if devices > are in order it will get enabled by default. Yeah, make sense. Besides, I have done some further profiling and debugging both in kernel driver and DPDK vhost. Previously I was mislead by a bug in vhost code. I will send a patch to fix that bug. With that bug fixed, the performance of packed ring in the test between kernel driver and DPDK vhost is better now. I will send a new series soon. Thanks! > > -- > MST _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
