[PATCH] D30941: Better testing of schedule model instruction latencies/throughputs

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In https://reviews.llvm.org/D30941#701498, @avt77 wrote:

> hfinkel, could you help me? First of all could you give me a link(s) to any doc(s) related to our MCSchedModel except sources?
>  Next, I was told that ResourceCycles here:
>  ===============================
>  class ProcWriteResources<list<ProcResourceKind> resources> {
>
>   list<ProcResourceKind> ProcResources = resources;
>   list<int> ResourceCycles = [];
>   int Latency = 1;
>   int NumMicroOps = 1;
>
> ================================
>  could be used as Throughput of the given instruction. Is it right? Does it mean I could include it in generated comment as well? If YES I suppose it should be the max of the Cycles, right?


I don't know if there are any docs besides the code and the code comments, but I think you are correct - the max of ResourceCycles is the inverse throughput for the instruction:

This is from include/llvm/Target/TargetSchedule.td :
// Optionally, ResourceCycles indicates the number of cycles the
// resource is consumed. Each ResourceCycles item is paired with the
// ProcResource item at the same position in its list. Since
// ResourceCycles are rarely specialized, the list may be
// incomplete. By default, resources are consumed for a single cycle,
// regardless of latency, which models a fully pipelined processing
// unit. A value of 0 for ResourceCycles means that the resource must
// be available but is not consumed, which is only relevant for
// unbuffered resources.

And this is in MachineScheduler.cpp:

  // For reserved resources, record the highest cycle using the resource.
  // For top-down scheduling, this is the cycle in which we schedule this
  // instruction plus the number of cycles the operations reserves the
  // resource.

We could abbreviate the comment string that you are adding like: [7:2].
I'm biased because that's the way I've always formatted [ latency : inverse throughput ], but I think that people that care about CPU timing will recognize that format, so you don't have to print out the words "latency" or "throughput".


https://reviews.llvm.org/D30941