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* [PATCH 1/2] powerpc/mm: Check for matching hpte without taking hpte lock
@ 2014-11-03 14:51 Aneesh Kumar K.V
  2014-11-03 14:51 ` [PATCH 2/2] powerpc/mm: don't do tlbie for updatepp request with NO HPTE fault Aneesh Kumar K.V
  0 siblings, 1 reply; 8+ messages in thread
From: Aneesh Kumar K.V @ 2014-11-03 14:51 UTC (permalink / raw)
  To: benh, paulus, mpe; +Cc: linuxppc-dev, Aneesh Kumar K.V

With smaller hash page table config, we would end up in situation
where we would be replacing hash page table slot frequently. In
such config, we will find the hpte to be not matching, and we
can do that check without holding the hpte lock. We need to
recheck the hpte again after holding lock.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 arch/powerpc/mm/hash_native_64.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/mm/hash_native_64.c b/arch/powerpc/mm/hash_native_64.c
index ae4962a06476..83c6bb12be14 100644
--- a/arch/powerpc/mm/hash_native_64.c
+++ b/arch/powerpc/mm/hash_native_64.c
@@ -294,8 +294,6 @@ static long native_hpte_updatepp(unsigned long slot, unsigned long newpp,
 	DBG_LOW("    update(vpn=%016lx, avpnv=%016lx, group=%lx, newpp=%lx)",
 		vpn, want_v & HPTE_V_AVPN, slot, newpp);
 
-	native_lock_hpte(hptep);
-
 	hpte_v = be64_to_cpu(hptep->v);
 	/*
 	 * We need to invalidate the TLB always because hpte_remove doesn't do
@@ -308,16 +306,24 @@ static long native_hpte_updatepp(unsigned long slot, unsigned long newpp,
 		DBG_LOW(" -> miss\n");
 		ret = -1;
 	} else {
-		DBG_LOW(" -> hit\n");
-		/* Update the HPTE */
-		hptep->r = cpu_to_be64((be64_to_cpu(hptep->r) & ~(HPTE_R_PP | HPTE_R_N)) |
-			(newpp & (HPTE_R_PP | HPTE_R_N | HPTE_R_C)));
+		native_lock_hpte(hptep);
+		/* recheck with locks held */
+		hpte_v = be64_to_cpu(hptep->v);
+		if (unlikely(!HPTE_V_COMPARE(hpte_v, want_v) ||
+			     !(hpte_v & HPTE_V_VALID))) {
+			ret = -1;
+		} else {
+			DBG_LOW(" -> hit\n");
+			/* Update the HPTE */
+			hptep->r = cpu_to_be64((be64_to_cpu(hptep->r) &
+						~(HPTE_R_PP | HPTE_R_N)) |
+					       (newpp & (HPTE_R_PP | HPTE_R_N |
+							 HPTE_R_C)));
+		}
+		native_unlock_hpte(hptep);
 	}
-	native_unlock_hpte(hptep);
-
 	/* Ensure it is out of the tlb too. */
 	tlbie(vpn, bpsize, apsize, ssize, local);
-
 	return ret;
 }
 
-- 
2.1.0

^ permalink raw reply related	[flat|nested] 8+ messages in thread
end of thread, other threads:[~2014-12-02  6:55 UTC | newest]

Thread overview: 8+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2014-11-03 14:51 [PATCH 1/2] powerpc/mm: Check for matching hpte without taking hpte lock Aneesh Kumar K.V
2014-11-03 14:51 ` [PATCH 2/2] powerpc/mm: don't do tlbie for updatepp request with NO HPTE fault Aneesh Kumar K.V
2014-12-01 23:59   ` Benjamin Herrenschmidt
2014-12-02  6:51     ` Aneesh Kumar K.V
2014-12-02  0:39   ` Michael Ellerman
2014-12-02  6:55     ` Aneesh Kumar K.V
2014-12-02  3:09   ` Benjamin Herrenschmidt
2014-12-02  5:01     ` Aneesh Kumar K.V

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