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[Xen-devel] Re: shared rings. rsp_cons, rsp_events, req_prod, req_events

To: Daniel Stodden <daniel.stodden@xxxxxxxxxx>
Subject: [Xen-devel] Re: shared rings. rsp_cons, rsp_events, req_prod, req_events docs, charts, timelines?
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Mon, 16 May 2011 17:16:19 -0400
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "keir@xxxxxxx" <keir@xxxxxxx>, "JBeulich@xxxxxxxxxx" <JBeulich@xxxxxxxxxx>
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On Mon, May 16, 2011 at 01:03:07PM -0700, Daniel Stodden wrote:
> On Mon, 2011-05-16 at 13:05 -0400, Konrad Rzeszutek Wilk wrote:
> > The current ring implementation uses these values and then macros such
> > as RING_HAS_UNCONSUMED_REQUESTS, FINAL_RING_CHECK, etc to determine whether
> > to continue or how to control the flow. Looking way back in the history
> > at c/s 8153 it used to have a 'server_is_sleeping' value to determine 
> > whether
> > to kick the back (now called 'req_event'), and the 'rsp_event' (unchanged)
> > to kick the frontend.
> > 
> > Anyhow, are there any diagrams or design docs documenting how these simple 
> > four
> > shared values help to control the pipeline and interrupt generation? Or how
> > they evolved over time to become what they are right now?
> Iirc, I've known these headers since late xen 2.x versions and never saw
> it done differently (i.e. req/rsp_event, and symmetrically).
> Never saw dedicated documentation either, but found the header comments
> and sources sufficient.
> Do you just want documentation to point at, or is there something not
> clear about them?

I was hoping to be able to double-check what I groked from the code. Figured
an example of the flow between frontend and backend over some time with
different scenarios would exist somwhere.

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