Another question about EXECLIST is: Can a preemption happen between element switch? I know this is beyond the scope of i915 a little. I'm just curious if it's possible. Let's say we have context A B C At first, we submit context A B in one ELSP write. Then, we submit context C in another ELSP write at some time. If context A or B is running and gets preempted, then there will be CSB.preempted in CSB buffer. This is the normal behavior. I'm wondering that if there is any possibility that a preemption can happen between the two elements. Then the CSB should look like: [CSB 0 idle-to-active] [CSB 1 CTX A element_switch/context_complete] [CSB 2 CTX C active-to-idle/context_complete] Is it possible? Thanks, Zhi. > -----Original Message----- > From: Thierry, Michel > Sent: Wednesday, November 25, 2015 8:48 PM > To: Wang, Zhi A; intel-gfx@xxxxxxxxxxxxxxxxxxxxx > Cc: Han, Xu; Li, Weinan Z; He, Min > Subject: Re: About dealing with CSB.context element switch in > execlist mode. > > On 11/24/2015 1:33 PM, Wang, Zhi A wrote: > > Hi Gurus: > > > > I'm wondering what's the right approach to deal with the context > > switch > > reason: element_switch? According to b-spec, one ELSP submission may > > include two elements, when one element is finished, HW will move to > > process next element, the previous context will be scheduled out with > > a "element_switch" context switch reason. > > Correct, in fact you get 2 flags, element_switch & context_complete. > > > > > I saw that i915 would try to start a new ELSP write which may contain > > two new elements when it found a "element_switch" CSB in the context > > switch handler. I'm a bit confused here, as HW may be still running a > > context at this time, I'm not sure if two new elements can be > > submitted at this time. So I think maybe my understanding about this > > context switch reason might be wrong. > > The driver is trying to speed up the execution when there are +3 contexts > queued. The first _new_ element you mention is in fact the running context. > > > > > Anyone can educate me how to deal with the "element_switch" CSB? > > > > Let's say you have contexts A, B, C and D already in queue, so A & B are > sent to the ELSP. > > After element_switch (A completed) B starts automatically, at this point > the driver will send a new execlist with B and C, effectively > lite-restoring B (note it cannot be a different context since that will > cause a preemption). > > And when B completes, the driver sends C & D. Lite-restoring the 2nd ctx > of each execlist allows us to send these 4 contexts with only 3 ELSP writes. > > > Thanks, > > > > Zhi. > > > -Michel _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
