From: "Michael S. Tsirkin" <mst@xxxxxxxxxx> Date: Wed, 1 Jun 2016 15:54:34 +0300 > This is in response to the proposal by Jason to make tun > rx packet queue lockless using a circular buffer. > My testing seems to show that at least for the common usecase > in networking, which isn't lockless, circular buffer > with indices does not perform that well, because > each index access causes a cache line to bounce between > CPUs, and index access causes stalls due to the dependency. > > By comparison, an array of pointers where NULL means invalid > and !NULL means valid, can be updated without messing up barriers > at all and does not have this issue. > > On the flip side, cache pressure may be caused by using large queues. > tun has a queue of 1000 entries by default and that's 8K. > At this point I'm not sure this can be solved efficiently. > The correct solution might be sizing the queues appropriately. > > Here's an implementation of this idea: it can be used more > or less whenever sk_buff_head can be used, except you need > to know the queue size in advance. ... I have no fundamental issues with this piece of infrastructure, but when it gets included I want this series to include at least one use case. This can be an adaptation of Jason's tun rx packet queue changes, or similar. Thanks. -- 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
