[WIP] Per-edge delays #2880

soheilshahrouz · 2025-02-03T18:44:56Z

This PR enables VPR to ingest a file that adds edge-specific delays to switch delays. This way, RR edges that represent the same switch type with the same fanin, can have different delays.

… new

…r_edge_attribute_offset_file()

…graph

…data

soheilshahrouz · 2025-02-03T18:53:45Z

A few notes:

In router lookahead construction, I decided to retrieve edge delay from switch type instead of using edge-specific dealys. I feel that using nominal switch delays, assuming they are average of per-edge delays of the same switch type, would make the router lookahead more translation invariant.
I think we should use per-edge delays to compute timing info for a routing tree. For this, RouteTreeNode needs to store the parent edge as well. This change is still to be implemented.
I see that some RouteTree methods like reload_timing_unlocked() and load_route_tree_Tdel() access swtich resistance and capacitance to calculate delay. Should we extent the input file format to enable overriding switch resistance and capacitance in addition to intrinsic delay?

vaughnbetz

Some thoughts on how to do this .... good to make a presentation on this for a Thursday meeting.

vaughnbetz · 2025-02-03T22:53:31Z

libs/libarchfpga/src/physical_types.h

@@ -1872,6 +1872,20 @@ struct t_rr_switch_inf {
    SwitchType type_ = SwitchType::INVALID;
 };

+struct t_rr_switch_offset_inf {


Suggest storing all the delay related info here, and not calling this offset (i.e. add in the basic switch delay too, if that's the way the files are supposed to work -- or maybe it's more clear to just override the default delay in a file rather than add to it).

vaughnbetz · 2025-02-03T22:57:36Z

libs/libarchfpga/src/physical_types.h

+    t_rr_switch_offset_inf(const t_rr_switch_inf& switch_inf)
+        : Tdel(switch_inf.Tdel) {}
+
+    auto operator<=>(const t_rr_switch_offset_inf&) const = default;


Give a comment on what your ordering will be, and why you need it.

vaughnbetz · 2025-02-03T22:58:42Z

libs/librrgraph/src/base/rr_graph_builder.h

        rr_switch_inf_.push_back(switch_info);

+        t_rr_switch_offset_inf switch_offset_info(switch_info);


Think of a better long term name -- rr_switch_flyweight? rr_switch_info?

vaughnbetz · 2025-02-03T22:59:22Z

libs/librrgraph/src/base/rr_graph_builder.h

@@ -315,6 +335,9 @@ class RRGraphBuilder {
    inline void reserve_switches(size_t num_switches) {
        this->rr_switch_inf_.reserve(num_switches);
    }
+    inline void reserve_switch_offse_info(size_t num_offsets) {


name mispelt?

vaughnbetz · 2025-02-03T23:05:14Z

libs/librrgraph/src/base/rr_graph_storage.cpp

@@ -354,6 +360,7 @@ void t_rr_graph_storage::assign_first_edges() {
    size_t num_edges = edge_src_node_.size();
    VTR_ASSERT(edge_dest_node_.size() == num_edges);
    VTR_ASSERT(edge_switch_.size() == num_edges);
+    VTR_ASSERT(edge_switch_offset_inf_.size() == num_edges);


I think one flyweight for edge data would be best, rather than two (switch_inf and edge_switch_offset_inf). Try to store one flyweight id per edge; we can set it up the same way as today during rr-graph building and then update it if the user requests that with an option saying they want a detailed delay file.

vaughnbetz · 2025-02-03T23:19:54Z

libs/librrgraph/src/io/rr_graph_uxsdcxx_serializer.h

@@ -2160,6 +2169,7 @@ class RrGraphSerializer final : public uxsd::RrGraphBase<RrGraphContextTypes> {
    RRGraphBuilder* rr_graph_builder_;
    RRGraphView* rr_graph_;
    vtr::vector<RRSwitchId, t_rr_switch_inf>* rr_switch_inf_;
+    vtr::vector<RRSwitchOffsetInfoId, t_rr_switch_offset_inf>* rr_switch_offset_inf_;


write out the new flyweight I think ... hard not to do that if we merge the flyweight.

vaughnbetz · 2025-02-03T23:23:19Z

vpr/src/base/SetupVPR.cpp

@@ -232,6 +232,7 @@ void SetupVPR(const t_options* options,
    SetupPackerOpts(*options, packerOpts);
    routingArch->write_rr_graph_filename = options->write_rr_graph_file;
    routingArch->read_rr_graph_filename = options->read_rr_graph_file;
+    routingArch->read_rr_edge_delay_offset_filename = options->read_rr_edge_delay_offset_file;


probably shouldn't call it offset -- detailed rr_delay file I think

vaughnbetz · 2025-02-03T23:23:31Z

vpr/src/base/read_options.cpp

@@ -1623,6 +1623,13 @@ argparse::ArgumentParser create_arg_parser(const std::string& prog_name, t_optio
        .metavar("RR_GRAPH_FILE")
        .show_in(argparse::ShowIn::HELP_ONLY);

+    file_grp.add_argument(args.read_rr_edge_delay_offset_file, "--read_rr_edge_delay_offset_file")


Offset -> detailed delay

vaughnbetz · 2025-02-03T23:24:35Z

vpr/src/base/vpr_types.h

@@ -1416,6 +1416,7 @@ struct t_det_routing_arch {
    float R_minW_pmos;

    std::string read_rr_graph_filename;
+    std::string read_rr_edge_delay_offset_filename;


delay_offset --> rename

vaughnbetz · 2025-02-03T23:26:51Z

vpr/src/route/connection_router.cpp

-    float switch_Tdel = rr_switch_inf_[iswitch].Tdel;
+    // Instead of looking up the delay from the RR switch type info,
+    // we call edge_delay() method that returns the exact delay calculated
+    // by adding edge-specific delays to the nominal delay of switch type


Test what the speed impact is of wrapping all the delay calculation functions in accessors, vs. getting an iswitch.
Might also be an opportunity to make the delay calculators more abstract.
Could make a method that returns a tuple of frequently used values in a hot loop if needed.

Also think about whether we should take the Elmore delay model out of the router, and just have a linear delay model that is abstracted (ask for an edge delay, get a delay and you don't know how)

…alls

soheilshahrouz · 2025-03-12T20:26:34Z

Superseded by #2930.

soheilshahrouz added 16 commits January 29, 2025 13:18

fix some typos in comments

1b306c0

cleaned print_switch_usage a little bit to use std::vector instead of…

9677848

… new

add RRGraphView::edge_delay

5bd1131

added t_rr_switch_offset_inf struct

af5a56e

finished the implementation of RRGraphView::edge_delay()

ea06ff4

add methods to RRGraphBuilder for modifying rr_switch_offset_inf_

e2321b5

add rr_switch_offset_inf argument to RRGraphView constructor

a03bfc0

partially implemented load_rr_edge_attribute_offset_file()

d4973a8

add RRGraphBuilder::set_edge_offset_id() method and call it in load_r…

8de3b3c

…r_edge_attribute_offset_file()

store actual unique delays instead of offsets

e0f3483

update edge_switch_offset_inf_ in the edge is already mapped

c6d6a40

create a t_rr_switch_offset_inf for each t_rr_switch_inf added to RR …

417bf61

…graph

init rr_switch_offset_inf_ when RR graph is read from a file

df1318b

add --read_rr_edge_delay_offset_file command line option

dda0e33

update rr_switch_offset_inf when rr_switch is updated based on fanin …

df6062c

…data

call edge_delay() instead of accessing switch delay

dd1df5c

github-actions bot added VPR VPR FPGA Placement & Routing Tool libarchfpga Library for handling FPGA Architecture descriptions lang-cpp C/C++ code libvtrutil labels Feb 3, 2025

soheilshahrouz added 5 commits February 3, 2025 13:55

Merge branch 'master' into per_edge_delay

412638f

clear edge_switch_offset_inf_ in RRGraphStorage

017abab

replace raw pointers with std::vector for seg_details_x/y

31f617a

replace t_clb_to_clb_directs* with std::vector<t_clb_to_clb_directs>&

91aed46

resize rr_switch_offset_inf_ and rr_switch_inf_ together

190f8b0

vaughnbetz reviewed Feb 3, 2025

View reviewed changes

soheilshahrouz added 3 commits February 5, 2025 11:14

rename t_rr_switch_offset_inf to t_rr_switch_override_inf

00739ed

add edge attribute methods

3cc543f

replace accesses to member vars of t_rr_switch with RRGraphView API c…

5bc080e

…alls

soheilshahrouz closed this Mar 12, 2025

soheilshahrouz deleted the per_edge_delay branch April 22, 2025 15:52

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

[WIP] Per-edge delays #2880

[WIP] Per-edge delays #2880

soheilshahrouz commented Feb 3, 2025

soheilshahrouz commented Feb 3, 2025

vaughnbetz left a comment

vaughnbetz Feb 3, 2025

vaughnbetz Feb 3, 2025

vaughnbetz Feb 3, 2025

vaughnbetz Feb 3, 2025

vaughnbetz Feb 3, 2025

vaughnbetz Feb 3, 2025

vaughnbetz Feb 3, 2025

vaughnbetz Feb 3, 2025

vaughnbetz Feb 3, 2025

vaughnbetz Feb 3, 2025

vaughnbetz Feb 3, 2025

soheilshahrouz commented Mar 12, 2025

		rr_switch_inf_.push_back(switch_info);

		t_rr_switch_offset_inf switch_offset_info(switch_info);

[WIP] Per-edge delays #2880

[WIP] Per-edge delays #2880

Conversation

soheilshahrouz commented Feb 3, 2025

soheilshahrouz commented Feb 3, 2025

vaughnbetz left a comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

Choose a reason for hiding this comment

soheilshahrouz commented Mar 12, 2025