Re: [Qemu-devel] [PATCH] implement moderation registers for e1000

[Luigi Rizzo]

On Fri, Feb 8, 2013 at 2:02 AM, Stefan Hajnoczi <address@hidden> 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).

cheers

luigi