On Sun, 10 Jul 2016 15:50:10 -0500 Tom Herbert <t...@herbertland.com> wrote:
> > This particular patch in the series is meant to be standalone exactly > > for this reason. I don't pretend to assert that this optimization will > > work for everybody, or even for a future version of me with different > > hardware. But, it passes my internal criteria for usefulness: > > 1. It provides a measurable gain in the experiments that I have at hand > > 2. The code is easy to review > > 3. The change does not negatively impact non-XDP users > > > > I would love to have a solution for all mlx4 driver users, but this > > patch set is focused on a different goal. So, without munging a > > different set of changes for the universal use case, and probably > > violating criteria #2 or #3, I went with what you see. > > > > In hopes of not derailing the whole patch series, what is an actionable > > next step for this patch #12? > > Ideas: > > Pick a safer N? (I saw improvements with N=1 as well) > > Drop this patch? > > > As Alexei mentioned the right prefetch model may be dependent on > workload. For instance, the XDP program for an ILA router is is far > less code path than packets going through TCP so it makes sense that > we would want different prefetch characteristics to optimize for each > case. Can we make this a configurable knob for each RX queue to allow > that? Please see my RFC patch[1] solution. I believe it solves the prefetch problem in a generic way, that both benefit XDP and the normal network stack. [1] http://thread.gmane.org/gmane.linux.network/420677/focus=420787 > > One thing I definitely don't want to do is go into the weeds trying to > > get a universal prefetch logic in order to merge the XDP framework, even > > though I agree the net result would benefit everybody. > > Agreed, a salient point of XDP is that it's _not_ a generic mechanism > meant for all applications. We don't want to sacrifice performance for > generality. I've just documented[2] that my generic solution does not sacrifice performance. [2] http://thread.gmane.org/gmane.linux.network/420677/focus=420999 -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer
