On Tue, Aug 16, 2016 at 1:54 PM, Francisco Jerez <curroje...@riseup.net>
wrote:
> This uses the unblocked time of the exit assigned to each available
> node to attempt to unblock exit nodes as early as possible,
> potentially reducing the runtime of the shader when an exit branch is
> taken. There is a natural trade-off between terminating the program
> as early as possible and reducing the worst-case latency of the
> program as a whole (since this will typically move exit-unblocking
> nodes closer to its dependencies potentially causing additional stalls
> of the execution pipeline), but in practice the bandwidth and ALU
> cycle savings from terminating the program earlier tend to outweigh
> the slight increase in worst-case program execution latency, so it
> makes sense to prefer nodes likely to unblock an earlier exit
> regardless of the latency benefits of other available nodes.
>
> I haven't observed any benchmark regressions from this change after
> testing on VLV, HSW, BDW, BSW and SKL. The FPS of the GfxBench
> Manhattan benchmark increases by 10%-20% and the FPS of Unigine Valley
> improves by roughly 5% depending on the platform and settings.
>
Thanks for working on this! We've known about it for a while and it's nice
to finally get some progress.
Reviewed-by: Jason Ekstrand <ja...@jlekstrand.net>
> The change to the register pressure-sensitive heuristic is rather
> conservative and gives precedence to the existing heuristic in order
> to avoid increasing register pressure and causing spill count and SIMD
> width regressions in shader-db. It may make sense to revisit this
> with additional performance data.
> ---
> .../drivers/dri/i965/brw_schedule_instructions.cpp | 19
> ++++++++++++++++---
> 1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
> b/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
> index 96562cf..dfcaa80 100644
> --- a/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
> @@ -1407,11 +1407,15 @@ fs_instruction_scheduler::choose_instruction_to_
> schedule()
> if (mode == SCHEDULE_PRE || mode == SCHEDULE_POST) {
> int chosen_time = 0;
>
> - /* Of the instructions ready to execute or the closest to
> - * being ready, choose the oldest one.
> + /* Of the instructions ready to execute or the closest to being
> ready,
> + * choose the one most likely to unblock an early program exit, or
> + * otherwise the oldest one.
> */
> foreach_in_list(schedule_node, n, &instructions) {
> - if (!chosen || n->unblocked_time < chosen_time) {
> + if (!chosen ||
> + exit_unblocked_time(n) < exit_unblocked_time(chosen) ||
> + (exit_unblocked_time(n) == exit_unblocked_time(chosen) &&
> + n->unblocked_time < chosen_time)) {
> chosen = n;
> chosen_time = n->unblocked_time;
> }
> @@ -1500,6 +1504,15 @@ fs_instruction_scheduler::choose_instruction_to_
> schedule()
> continue;
> }
>
> + /* Prefer the node most likely to unblock an early program exit.
> + */
> + if (exit_unblocked_time(n) < exit_unblocked_time(chosen)) {
> + chosen = n;
> + continue;
> + } else if (exit_unblocked_time(n) > exit_unblocked_time(chosen))
> {
> + continue;
> + }
> +
> /* If all other metrics are equal, we prefer the first
> instruction in
> * the list (program execution).
> */
> --
> 2.9.0
>
> _______________________________________________
> mesa-dev mailing list
> mesa-dev@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>
_______________________________________________
mesa-dev mailing list
mesa-dev@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/mesa-dev
