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Date:      Tue, 26 Feb 2019 09:45:45 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r344572 - in head/sys/i386: i386 include
Message-ID:  <201902260945.x1Q9jj4x009414@repo.freebsd.org>
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Author: kib
Date: Tue Feb 26 09:45:44 2019
New Revision: 344572
URL: https://svnweb.freebsd.org/changeset/base/344572

Log:
  i386 PAE: avoid atomic for pte_store() where possible.
  
  Instead carefully write upper word, and only than the lower word with
  PG_V, for previously invalid ptes.  It provides some measurable system
  time saving on buildworld.
  
  Reviewed by:	markj
  Tested by:	pho
  Measured by:	bde (early version)
  Sponsored by:	The FreeBSD Foundation
  Differential revision:	https://reviews.freebsd.org/D19226

Modified:
  head/sys/i386/i386/pmap.c
  head/sys/i386/include/pmap_nopae.h
  head/sys/i386/include/pmap_pae.h

Modified: head/sys/i386/i386/pmap.c
==============================================================================
--- head/sys/i386/i386/pmap.c	Tue Feb 26 09:44:10 2019	(r344571)
+++ head/sys/i386/i386/pmap.c	Tue Feb 26 09:45:44 2019	(r344572)
@@ -3801,7 +3801,7 @@ validate:
 		if ((origpte & PG_A) != 0)
 			pmap_invalidate_page_int(pmap, va);
 	} else
-		pte_store(pte, newpte);
+		pte_store_zero(pte, newpte);
 
 unchanged:
 
@@ -4104,7 +4104,7 @@ pmap_enter_quick_locked(pmap_t pmap, vm_offset_t va, v
 #endif
 	if (pmap != kernel_pmap)
 		newpte |= PG_U;
-	pte_store(pte, newpte);
+	pte_store_zero(pte, newpte);
 	sched_unpin();
 	return (mpte);
 }

Modified: head/sys/i386/include/pmap_nopae.h
==============================================================================
--- head/sys/i386/include/pmap_nopae.h	Tue Feb 26 09:44:10 2019	(r344571)
+++ head/sys/i386/include/pmap_nopae.h	Tue Feb 26 09:45:44 2019	(r344572)
@@ -86,6 +86,7 @@ typedef	uint32_t pdpt_entry_t;	/* Only to keep struct 
 #define	pte_store(ptep, pte) do { \
 	*(u_int *)(ptep) = (u_int)(pte); \
 } while (0)
+#define	pte_store_zero(ptep, pte)	pte_store(ptep, pte)
 #define	pte_load(ptep)			atomic_load_int(ptep)
 
 extern pt_entry_t PTmap[];

Modified: head/sys/i386/include/pmap_pae.h
==============================================================================
--- head/sys/i386/include/pmap_pae.h	Tue Feb 26 09:44:10 2019	(r344571)
+++ head/sys/i386/include/pmap_pae.h	Tue Feb 26 09:45:44 2019	(r344572)
@@ -101,6 +101,16 @@ typedef uint64_t pt_entry_t;
 #define	pte_load_store(ptep, pte)	atomic_swap_64_i586(ptep, pte)
 #define	pte_load_clear(ptep)		atomic_swap_64_i586(ptep, 0)
 #define	pte_store(ptep, pte)		atomic_store_rel_64_i586(ptep, pte)
+#define	pte_store_zero(ptep, pte)		\
+do {						\
+	uint32_t *p;				\
+						\
+	MPASS((*ptep & PG_V) == 0);		\
+	p = (void *)ptep;			\
+	*(p + 1) = (uint32_t)(pte >> 32);	\
+	__compiler_membar();			\
+	*p = (uint32_t)pte;			\
+} while (0)
 #define	pte_load(ptep)			atomic_load_acq_64_i586(ptep)
 
 extern pdpt_entry_t *IdlePDPT;

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