On Fri, Feb 8, 2013 at 11:46 AM, Paolo Bonzini <pbonz...@redhat.com> wrote: > Il 08/02/2013 11:20, Luigi Rizzo ha scritto: >> On Fri, Feb 8, 2013 at 2:02 AM, Stefan Hajnoczi <stefa...@gmail.com >> <mailto:stefa...@gmail.com>> wrote: >> >> On Wed, Feb 06, 2013 at 03:23:41PM +0100, Luigi Rizzo wrote: >> > The following patch implements interrupt moderation registers >> > for the e1000 adapter. These feature is normally used by OS >> > drivers, and their implementation improves performance significantly, >> > especially on the transmit path. >> > The feature can be disabled through a command line option. >> > We have seen only benefits in throughput, while latency slightly >> > increases (that is an inherent feature of interrupt moderation) >> > because very short delays cannot be emulated precisely. >> > >> > For those curious on performance, there is a set of measurements >> > (of this and other changes that we will post separately) at >> > >> > http://info.iet.unipi.it/~luigi/research.html#qemu >> >> http://info.iet.unipi.it/~luigi/papers/20130206-qemu.pdf is 404. >> >> >> sorry, fixed now. >> And, will resubmit a fixed patch with uninit and fixed braces in the >> if() statement. >> >> I am happy to make this default to off. But it would be good if you could >> actually give it a try. Note that linux and FreeBSD (and presumably windows) >> do use moderation by default so enabling the emulation of the >> registers makes the guest OS behave differently (and closer to bare metal). >> >> To test that the patch itself does not cause regression in the emulator >> one should also turn off moderation in the guest (one of the tests i >> have run). > > I think making the default on is fine, but you need to add compatibility > options to leave it off in older machine types (pc-1.4 and earlier).
Latency regression. Would need to see real results to understand how bad it is. Stefan
