Dave Airlie wrote: >> I'm trying to figure out how context switches acutally work... the DRI >> lock is overloaded as context switcher, and there is code in the >> kernel to call out to a chipset specific context switch routine when >> the DRI lock is taken... but only ffb uses it... So I'm guessing the >> way context switches work today is that the DRI driver grabs the lock >> and after potentially updating the cliprects through X protocol, it >> emits all the state it depends on to the cards. Is the state emission >> done by just writing out a bunch of registers? Is this how the X >> server works too, except XAA/EXA acceleration doesn't depend on a lot >> of state and thus the DDX driver can emit everything for each >> operation? >> > > So yes userspaces notices context has changed and just re-emits everything > into the batchbuffer it is going to send, for XAA/EXA stuff in Intel at > least there is an invarient state emission functions that notices what the > context was and what the last server 3D users was (EXA or Xv texturing) > and just dumps the state into the batchbuffer.. (or currently into the > ring) > > >> How would this work if we didn't have a lock? You can't emit the >> state and then start rendering without a lock to keep the state in >> place... If the kernel doesn't restore any state, whats the point of >> the drm_context_t we pass to the kernel in drmLock? Should the kernel >> know how to restore state (this ties in to the email from jglisse on >> state tracking in drm and all the gallium jazz, I guess)? How do we >> identify state to the kernel, and how do we pass it in in the >> super-ioctl? Can we add a list of registers to be written and the >> values? I talked to Dave about it and we agreed that adding a >> drm_context_t to the super-ioctl would work, but now I'm thinking if >> the kernel doesn't track any state it wont really work. Maybe >> cross-client state sharing isn't useful for performance as Keith and >> Roland argues, but if the kernel doesn't restore state when it sees a >> super-ioctl coming from a different context, who does? >> >> > > My guess for one way is to store a buffer object with the current state > emission in it, and submit it with the superioctl maybe, and if we have > lost context emit it before the batchbuffer.. > > There are probably various ways to do this, which is another argument for keeping super-ioctls device-specific. For i915-type hardware, Dave's approach above is probably the most attracting one. For Poulsbo, all state is always implicitly included, usually as a reference to a buffer object, so we don't really bother about contexts here. For hardware like the Unichrome, the state is stored in a limited set of registers. Here the drm can keep a copy of those registers for each context and do a smart update on a context switch.
However, there are cases where it is very difficult to use cliprects from the drm, though I wouldn't say impossible. /Thomas > Dave. > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Microsoft > Defy all challenges. Microsoft(R) Visual Studio 2005. > http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ > -- > _______________________________________________ > Dri-devel mailing list > Dri-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/dri-devel > ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel
