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Date:      Tue, 20 Apr 2010 22:59:56 +0000 (UTC)
From:      Kip Macy <kmacy@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-user@freebsd.org
Subject:   svn commit: r206953 - in user/kmacy/head_page_lock_2/sys/amd64: amd64 include
Message-ID:  <201004202259.o3KMxuJN070901@svn.freebsd.org>
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Author: kmacy
Date: Tue Apr 20 22:59:56 2010
New Revision: 206953
URL: http://svn.freebsd.org/changeset/base/206953

Log:
  - handle multiple simultaneous relocks on a pmap using a counter
  - only return EAGAIN if the pmap lock was acquired by another caller
    in the meantime or another caller is in the middle of a retry

Modified:
  user/kmacy/head_page_lock_2/sys/amd64/amd64/pmap.c
  user/kmacy/head_page_lock_2/sys/amd64/include/pmap.h

Modified: user/kmacy/head_page_lock_2/sys/amd64/amd64/pmap.c
==============================================================================
--- user/kmacy/head_page_lock_2/sys/amd64/amd64/pmap.c	Tue Apr 20 22:57:05 2010	(r206952)
+++ user/kmacy/head_page_lock_2/sys/amd64/amd64/pmap.c	Tue Apr 20 22:59:56 2010	(r206953)
@@ -213,6 +213,10 @@ static int pmap_tryrelock_restart;
 SYSCTL_INT(_vm_pmap, OID_AUTO, tryrelock_restart, CTLFLAG_RD,
     &pmap_tryrelock_restart, 0, "Number of tryrelock restarts");
 
+static int pmap_tryrelock_race;
+SYSCTL_INT(_vm_pmap, OID_AUTO, tryrelock_race, CTLFLAG_RD,
+    &pmap_tryrelock_race, 0, "Number of tryrelock pmap race cases");
+
 
 static u_int64_t	KPTphys;	/* phys addr of kernel level 1 */
 static u_int64_t	KPDphys;	/* phys addr of kernel level 2 */
@@ -549,8 +553,10 @@ static int
 pa_tryrelock(pmap_t pmap, vm_paddr_t pa, vm_paddr_t *locked)
 {
 	vm_paddr_t lockpa;
+	uint16_t gen_count;
 
 	PMAP_LOCK_ASSERT(pmap, MA_OWNED);
+	gen_count = pmap->pm_gen_count;
 	atomic_add_long((volatile long *)&pmap_tryrelock_calls, 1);
 	lockpa = *locked;
 	*locked = pa;
@@ -562,14 +568,20 @@ pa_tryrelock(pmap_t pmap, vm_paddr_t pa,
 	}
 	if (PA_TRYLOCK(pa))
 		return (0);
-	pmap->pm_flags |= PMAP_IN_RETRY;
+	pmap->pm_retry_depth++;
 	PMAP_UNLOCK(pmap);
 	atomic_add_int((volatile int *)&pmap_tryrelock_restart, 1);
 	PA_LOCK(pa);
 	mtx_lock(&(pmap)->pm_mtx);
-	pmap->pm_flags &= ~PMAP_IN_RETRY;
-
-	return (EAGAIN);
+	pmap->pm_retry_depth--;
+	if (pmap->pm_retry_depth)
+		pmap->pm_gen_count++;
+
+	if (gen_count != pmap->pm_gen_count) {
+		atomic_add_int((volatile int *)&pmap_tryrelock_race, 1);
+		return (EAGAIN);
+	}
+	return (0);
 }
 
 static u_int64_t

Modified: user/kmacy/head_page_lock_2/sys/amd64/include/pmap.h
==============================================================================
--- user/kmacy/head_page_lock_2/sys/amd64/include/pmap.h	Tue Apr 20 22:57:05 2010	(r206952)
+++ user/kmacy/head_page_lock_2/sys/amd64/include/pmap.h	Tue Apr 20 22:59:56 2010	(r206953)
@@ -237,8 +237,6 @@ struct md_page {
 	int			pat_mode;
 };
 
-#define PMAP_IN_RETRY		0x1
-
 /*
  * The kernel virtual address (KVA) of the level 4 page table page is always
  * within the direct map (DMAP) region.
@@ -249,7 +247,7 @@ struct pmap {
 	TAILQ_HEAD(,pv_chunk)	pm_pvchunk;	/* list of mappings in pmap */
 	u_int			pm_active;	/* active on cpus */
 	uint16_t		pm_gen_count;	/* generation count (pmap lock dropped) */
-	uint16_t		pm_flags;
+	uint16_t		pm_retry_depth;	/* number of cases in retry */
 	struct pmap_statistics	pm_stats;	/* pmap statistics */
 	vm_page_t		pm_root;	/* spare page table pages */
 	vm_page_t		pm_free;	/* Temporary free pages. */
@@ -263,7 +261,7 @@ extern struct pmap	kernel_pmap_store;
 
 #define PMAP_UPDATE_GEN_COUNT(pmap)				\
 	do {							\
-		if (pmap->pm_flags & PMAP_IN_RETRY)		\
+		if (pmap->pm_retry_depth)			\
 			pmap->pm_gen_count++;			\
 	} while (0)

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