Re: Add prefetch switch stack hook in scheduler function

* Eric Dumazet <[email protected]> wrote:

> Please test that len is a constant, or else the inlining is too large 
> for the non constant case.

yeah. fix below.

	Ingo

-----
noticed by Eric Dumazet: unrolling should be dependent on a constant
length, otherwise inlining gets too large.

Signed-off-by: Ingo Molnar <[email protected]>

 include/linux/prefetch.h |  128 ++++++++++++++++++++++++-----------------------
 1 files changed, 66 insertions(+), 62 deletions(-)

Index: linux-prefetch-task/include/linux/prefetch.h
===================================================================
--- linux-prefetch-task.orig/include/linux/prefetch.h
+++ linux-prefetch-task/include/linux/prefetch.h
@@ -64,37 +64,39 @@ static inline void prefetch_range(void *
 	/*
 	 * Unroll agressively:
 	 */
-	if (len <= PREFETCH_STRIDE)
-		prefetch(cp);
-	else if (len <= 2*PREFETCH_STRIDE) {
-		prefetch(cp);
-		prefetch(cp + PREFETCH_STRIDE);
-	}
-	else if (len <= 3*PREFETCH_STRIDE) {
-		prefetch(cp);
-		prefetch(cp + PREFETCH_STRIDE);
-		prefetch(cp + 2*PREFETCH_STRIDE);
-	}
-	else if (len <= 4*PREFETCH_STRIDE) {
-		prefetch(cp);
-		prefetch(cp + PREFETCH_STRIDE);
-		prefetch(cp + 2*PREFETCH_STRIDE);
-		prefetch(cp + 3*PREFETCH_STRIDE);
-	}
-	else if (len <= 5*PREFETCH_STRIDE) {
-		prefetch(cp);
-		prefetch(cp + PREFETCH_STRIDE);
-		prefetch(cp + 2*PREFETCH_STRIDE);
-		prefetch(cp + 3*PREFETCH_STRIDE);
-		prefetch(cp + 4*PREFETCH_STRIDE);
-	}
-	else if (len <= 6*PREFETCH_STRIDE) {
-		prefetch(cp);
-		prefetch(cp + PREFETCH_STRIDE);
-		prefetch(cp + 2*PREFETCH_STRIDE);
-		prefetch(cp + 3*PREFETCH_STRIDE);
-		prefetch(cp + 4*PREFETCH_STRIDE);
-		prefetch(cp + 5*PREFETCH_STRIDE);
+	if (__builtin_constant_p(len) && (len <= 6*PREFETCH_STRIDE)) {
+		if (len <= PREFETCH_STRIDE)
+			prefetch(cp);
+		else if (len <= 2*PREFETCH_STRIDE) {
+			prefetch(cp);
+			prefetch(cp + PREFETCH_STRIDE);
+		}
+		else if (len <= 3*PREFETCH_STRIDE) {
+			prefetch(cp);
+			prefetch(cp + PREFETCH_STRIDE);
+			prefetch(cp + 2*PREFETCH_STRIDE);
+		}
+		else if (len <= 4*PREFETCH_STRIDE) {
+			prefetch(cp);
+			prefetch(cp + PREFETCH_STRIDE);
+			prefetch(cp + 2*PREFETCH_STRIDE);
+			prefetch(cp + 3*PREFETCH_STRIDE);
+		}
+		else if (len <= 5*PREFETCH_STRIDE) {
+			prefetch(cp);
+			prefetch(cp + PREFETCH_STRIDE);
+			prefetch(cp + 2*PREFETCH_STRIDE);
+			prefetch(cp + 3*PREFETCH_STRIDE);
+			prefetch(cp + 4*PREFETCH_STRIDE);
+		}
+		else if (len <= 6*PREFETCH_STRIDE) {
+			prefetch(cp);
+			prefetch(cp + PREFETCH_STRIDE);
+			prefetch(cp + 2*PREFETCH_STRIDE);
+			prefetch(cp + 3*PREFETCH_STRIDE);
+			prefetch(cp + 4*PREFETCH_STRIDE);
+			prefetch(cp + 5*PREFETCH_STRIDE);
+		}
 	} else
 		for (; cp < end; cp += PREFETCH_STRIDE)
 			prefetch(cp);
@@ -110,37 +112,39 @@ static inline void prefetchw_range(void 
 	/*
 	 * Unroll agressively:
 	 */
-	if (len <= PREFETCH_STRIDE)
-		prefetchw(cp);
-	else if (len <= 2*PREFETCH_STRIDE) {
-		prefetchw(cp);
-		prefetchw(cp + PREFETCH_STRIDE);
-	}
-	else if (len <= 3*PREFETCH_STRIDE) {
-		prefetchw(cp);
-		prefetchw(cp + PREFETCH_STRIDE);
-		prefetchw(cp + 2*PREFETCH_STRIDE);
-	}
-	else if (len <= 4*PREFETCH_STRIDE) {
-		prefetchw(cp);
-		prefetchw(cp + PREFETCH_STRIDE);
-		prefetchw(cp + 2*PREFETCH_STRIDE);
-		prefetchw(cp + 3*PREFETCH_STRIDE);
-	}
-	else if (len <= 5*PREFETCH_STRIDE) {
-		prefetchw(cp);
-		prefetchw(cp + PREFETCH_STRIDE);
-		prefetchw(cp + 2*PREFETCH_STRIDE);
-		prefetchw(cp + 3*PREFETCH_STRIDE);
-		prefetchw(cp + 4*PREFETCH_STRIDE);
-	}
-	else if (len <= 6*PREFETCH_STRIDE) {
-		prefetchw(cp);
-		prefetchw(cp + PREFETCH_STRIDE);
-		prefetchw(cp + 2*PREFETCH_STRIDE);
-		prefetchw(cp + 3*PREFETCH_STRIDE);
-		prefetchw(cp + 4*PREFETCH_STRIDE);
-		prefetchw(cp + 5*PREFETCH_STRIDE);
+	if (__builtin_constant_p(len) && (len <= 6*PREFETCH_STRIDE)) {
+		if (len <= PREFETCH_STRIDE)
+			prefetchw(cp);
+		else if (len <= 2*PREFETCH_STRIDE) {
+			prefetchw(cp);
+			prefetchw(cp + PREFETCH_STRIDE);
+		}
+		else if (len <= 3*PREFETCH_STRIDE) {
+			prefetchw(cp);
+			prefetchw(cp + PREFETCH_STRIDE);
+			prefetchw(cp + 2*PREFETCH_STRIDE);
+		}
+		else if (len <= 4*PREFETCH_STRIDE) {
+			prefetchw(cp);
+			prefetchw(cp + PREFETCH_STRIDE);
+			prefetchw(cp + 2*PREFETCH_STRIDE);
+			prefetchw(cp + 3*PREFETCH_STRIDE);
+		}
+		else if (len <= 5*PREFETCH_STRIDE) {
+			prefetchw(cp);
+			prefetchw(cp + PREFETCH_STRIDE);
+			prefetchw(cp + 2*PREFETCH_STRIDE);
+			prefetchw(cp + 3*PREFETCH_STRIDE);
+			prefetchw(cp + 4*PREFETCH_STRIDE);
+		}
+		else if (len <= 6*PREFETCH_STRIDE) {
+			prefetchw(cp);
+			prefetchw(cp + PREFETCH_STRIDE);
+			prefetchw(cp + 2*PREFETCH_STRIDE);
+			prefetchw(cp + 3*PREFETCH_STRIDE);
+			prefetchw(cp + 4*PREFETCH_STRIDE);
+			prefetchw(cp + 5*PREFETCH_STRIDE);
+		}
 	} else
 		for (; cp < end; cp += PREFETCH_STRIDE)
 			prefetchw(cp);
-
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---

• References:
  • Re: Add prefetch switch stack hook in scheduler function
    • From: Ingo Molnar <[email protected]>
  • RE: Add prefetch switch stack hook in scheduler function
    • From: "Chen, Kenneth W" <[email protected]>
  • Re: Add prefetch switch stack hook in scheduler function
    • From: Ingo Molnar <[email protected]>
  • Re: Add prefetch switch stack hook in scheduler function
    • From: Ingo Molnar <[email protected]>
  • Re: Add prefetch switch stack hook in scheduler function
    • From: Eric Dumazet <[email protected]>

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