Date: Thu, 22 Jan 2015 11:03:24 -0800 From: Luigi Rizzo <rizzo@iet.unipi.it> To: Ciprian Barbu <ciprian.barbu@linaro.org> Cc: "freebsd-net@freebsd.org" <net@freebsd.org> Subject: Re: Netmap mempool Message-ID: <CA%2BhQ2%2BhUzPofZRC_zAD7r4gGxuW09EBAsA9CCBcfOOX3qTrG2Q@mail.gmail.com> In-Reply-To: <CADJJ_HZzevQy9891qnOgyiDz5xeGC%2BQFjhZBh-URmcmUs83nhA@mail.gmail.com> References: <CADJJ_HZzevQy9891qnOgyiDz5xeGC%2BQFjhZBh-URmcmUs83nhA@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Thu, Jan 22, 2015 at 10:12 AM, Ciprian Barbu <ciprian.barbu@linaro.org> wrote: > Hello, > > I have some questions related to OpenDataPlane. I have implemented the > I/O access using netmap for ODP but currently it's suffering from low > performance due to packets being copied between the netmap slots and > ODP buffers. > > I want to create ODP buffer pools on top of netmap memory but I'm > concerned with three things: > 1. how to keep a buffer for as long as needed without affecting the > receive process; I guess I could use the NS_BUF_CHANGED flag in some > way > 2. the netmap memory may not be large enough to accommodate a complex > ODP application > 3. the ODP application may occasionally hold on to buffers for longer time > there is a way to hold buffers without returning them to the ring using the 'cur' pointer in the ring, see the netmap manpage how this is implemented and how it works on the tx and rx path. However, before embarking in zero copy i'd like you to elaborate on what you mean for "low performance" (how many pps you see) and what are your expectations. In my experience low performance almost always comes from insufficient batching or other application bottlenecks. Zero copy tricks come with great complications to track who owns what, sometimes with additional hidden overhead (e.g. if you change buffers the driver has to reprogram the IOMMU) and often have a very limited effect in real world applications. Sure the numbers do look good on benchmarks or academic papers, but there people don't worry about robustness and code maintainability. cheers luigi
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CA%2BhQ2%2BhUzPofZRC_zAD7r4gGxuW09EBAsA9CCBcfOOX3qTrG2Q>