On Tue, Jan 03, 2012 at 03:38:25PM -0800, Keith Packard wrote: > On Wed, 4 Jan 2012 00:04:18 +0100, Daniel Vetter <daniel at ffwll.ch> wrote: > > > I kinda prefer Chris' approach of sticking with irqs, but backing it up > > with a timer in the msec range. Can't find that patch though atm (iirc > > it's in bugzilla somewhere). > > I think we've resolved that the interrupt arrives, but that it is not > serialized wrt the memory write. So, what I'd love to see is whether > waiting for the irq and then busy looping for 'a while' works. This > would allow for long-running operations to idle the CPU and then hit the > interrupt and spin until the memory write is recognized. > > Any solution which can leave operations unacknowledged for 'ms' > timeframes seems like a potential for serious performance > problems. Eric's simple spinning approach seems fine for the BLT ring > which we don't use that often; something more complicated and yet not > entirely timer-based might be more efficient for longer-running operations. Afaics we only spin shortly on the blt ring if - semaphores are not enabled and - mesa is the client. For all other cases it's pretty easy to come up with examples where we busy-loop for a rather long time. So I really don't like the busy-looping, especially now that semaphores are enabled by default for ivb. -Daniel -- Daniel Vetter Mail: daniel at ffwll.ch Mobile: +41 (0)79 365 57 48
