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Date:      Sat, 31 Jul 2010 21:35:16 +0000 (UTC)
From:      Nathan Whitehorn <nwhitehorn@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r210704 - in head/sys/powerpc: aim include
Message-ID:  <201007312135.o6VLZG2p000437@svn.freebsd.org>
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Author: nwhitehorn
Date: Sat Jul 31 21:35:15 2010
New Revision: 210704
URL: http://svn.freebsd.org/changeset/base/210704

Log:
  Improve hash coverage for kernel page table entries by modifying the kernel
  ESID -> VSID map function. This makes ZFS run stably on PowerPC under
  heavy loads (repeated simultaneous SVN checkouts and updates).

Modified:
  head/sys/powerpc/aim/mmu_oea64.c
  head/sys/powerpc/aim/slb.c
  head/sys/powerpc/include/slb.h

Modified: head/sys/powerpc/aim/mmu_oea64.c
==============================================================================
--- head/sys/powerpc/aim/mmu_oea64.c	Sat Jul 31 21:33:18 2010	(r210703)
+++ head/sys/powerpc/aim/mmu_oea64.c	Sat Jul 31 21:35:15 2010	(r210704)
@@ -838,7 +838,7 @@ moea64_bootstrap_slb_prefault(vm_offset_
 	}
 
 	entry.slbe = slbe;
-	entry.slbv = KERNEL_VSID(esid, large) << SLBV_VSID_SHIFT;
+	entry.slbv = KERNEL_VSID(esid) << SLBV_VSID_SHIFT;
 	if (large)
 		entry.slbv |= SLBV_L;
 

Modified: head/sys/powerpc/aim/slb.c
==============================================================================
--- head/sys/powerpc/aim/slb.c	Sat Jul 31 21:33:18 2010	(r210703)
+++ head/sys/powerpc/aim/slb.c	Sat Jul 31 21:35:15 2010	(r210704)
@@ -104,17 +104,10 @@ uint64_t
 va_to_vsid(pmap_t pm, vm_offset_t va)
 {
 	struct slb entry;
-	int large;
 
 	/* Shortcut kernel case */
-	if (pm == kernel_pmap) {
-		large = 0;
-		if (hw_direct_map && va < VM_MIN_KERNEL_ADDRESS &&
-		    mem_valid(va, 0) == 0)
-			large = 1;
-
-		return (KERNEL_VSID((uintptr_t)va >> ADDR_SR_SHFT, large));
-	}
+	if (pm == kernel_pmap)
+		return (KERNEL_VSID((uintptr_t)va >> ADDR_SR_SHFT));
 
 	/*
 	 * If there is no vsid for this VA, we need to add a new entry

Modified: head/sys/powerpc/include/slb.h
==============================================================================
--- head/sys/powerpc/include/slb.h	Sat Jul 31 21:33:18 2010	(r210703)
+++ head/sys/powerpc/include/slb.h	Sat Jul 31 21:35:15 2010	(r210704)
@@ -47,14 +47,15 @@
 #define	SLBV_VSID_MASK	0xfffffffffffff000UL /* Virtual segment ID mask */
 #define	SLBV_VSID_SHIFT	12
 
-#define	KERNEL_VSID_BIT	0x0000001000000000UL /* Bit set in all kernel VSIDs */
-
 /*
- * Shift large-page VSIDs one place left. At present, they are only used in the
- * kernel direct map, and we already assume in the placement of KVA that the
- * CPU cannot address more than 63 bits of memory.
+ * Make a predictable 1:1 map from ESIDs to VSIDs for the kernel. Hash table
+ * coverage is increased by swizzling the ESID and multiplying by a prime
+ * number (0x13bb).
  */
-#define KERNEL_VSID(esid, large) (((uint64_t)(esid) << (large ? 1 : 0)) | KERNEL_VSID_BIT)
+#define	KERNEL_VSID_BIT	0x0000001000000000UL /* Bit set in all kernel VSIDs */
+#define KERNEL_VSID(esid) ((((((uint64_t)esid << 8) | ((uint64_t)esid >> 28)) \
+				* 0x13bbUL) & (KERNEL_VSID_BIT - 1)) | \
+				KERNEL_VSID_BIT)
 
 #define	SLBE_VALID	0x0000000008000000UL /* SLB entry valid */
 #define	SLBE_INDEX_MASK	0x0000000000000fffUL /* SLB index mask*/

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