Skip to content

[SamplePGO] Add a cutoff for number of profile matching anchors #95542

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Jun 17, 2024
Merged

[SamplePGO] Add a cutoff for number of profile matching anchors #95542

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
16 changes: 16 additions & 0 deletions llvm/lib/Transforms/IPO/SampleProfileMatcher.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
#include "llvm/Transforms/IPO/SampleProfileMatcher.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/Support/CommandLine.h"

using namespace llvm;
using namespace sampleprof;
Expand All @@ -24,6 +25,11 @@ extern cl::opt<bool> SalvageStaleProfile;
extern cl::opt<bool> PersistProfileStaleness;
extern cl::opt<bool> ReportProfileStaleness;

static cl::opt<unsigned> SalvageStaleProfileMaxCallsites(
"salvage-stale-profile-max-callsites", cl::Hidden, cl::init(UINT_MAX),
cl::desc("The maximum number of callsites in a function, above which stale "
"profile matching will be skipped."));

void SampleProfileMatcher::findIRAnchors(const Function &F,
AnchorMap &IRAnchors) {
// For inlined code, recover the original callsite and callee by finding the
Expand Down Expand Up @@ -300,6 +306,16 @@ void SampleProfileMatcher::runStaleProfileMatching(
if (FilteredIRAnchorsList.empty() || FilteredProfileAnchorList.empty())
return;

if (FilteredIRAnchorsList.size() > SalvageStaleProfileMaxCallsites ||
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Is it necessary to check both anchor list size or just one?

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Since this check is meant to prevent superlinear behaviour in case of very large functions, I think it makes sense to check for both "the profile has too many anchors" and "the IR has too many anchors". In the regular case both should be small and cases where any of those is say >1000 are exotic enough that it might be better to err on the side of caution and skip those functions.

For example: those functions are often autogenerated, in which case stale profile matching (which targets localised edits made by humans) might not be very appropriate.

Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

should the default to be something other than UINT_MAX?

FilteredProfileAnchorList.size() > SalvageStaleProfileMaxCallsites) {
LLVM_DEBUG(dbgs() << "Skip stale profile matching for " << F.getName()
<< " because the number of callsites in the IR is "
<< FilteredIRAnchorsList.size()
<< " and in the profile is "
<< FilteredProfileAnchorList.size() << "\n");
return;
}

// Match the callsite anchors by finding the longest common subsequence
// between IR and profile. Note that we need to use IR anchor as base(A side)
// to align with the order of IRToProfileLocationMap.
Expand Down
3 changes: 3 additions & 0 deletions llvm/test/Transforms/SampleProfile/pseudo-probe-stale-profile-matching-LCS.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
; REQUIRES: x86_64-linux
; REQUIRES: asserts
; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/pseudo-probe-stale-profile-matching-LCS.prof --salvage-stale-profile -S --debug-only=sample-profile,sample-profile-matcher,sample-profile-impl 2>&1 | FileCheck %s
; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/pseudo-probe-stale-profile-matching-LCS.prof --salvage-stale-profile -S --debug-only=sample-profile,sample-profile-matcher,sample-profile-impl --salvage-stale-profile-max-callsites=6 2>&1 | FileCheck %s -check-prefix=CHECK-MAX-CALLSITES

; CHECK: Run stale profile matching for test_direct_call
; CHECK: Location is matched from 1 to 1
Expand All @@ -27,6 +28,8 @@
; CHECK: Callsite with callee:unknown.indirect.callee is matched from 9 to 6
; CHECK: Callsite with callee:C is matched from 10 to 7

; CHECK-MAX-CALLSITES: Skip stale profile matching for test_direct_call
; CHECK-MAX-CALLSITES-NOT: Skip stale profile matching for test_indirect_call

target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
Expand Down
Loading