linux-kernel - [34-longterm 140/260] Optimize ticket spinlocks in fsys_rt

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Message-Id: <1293952756-15010-141-git-send-email-paul.gortmaker@windriver.com>
Date:	Sun,  2 Jan 2011 02:17:16 -0500
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	stable@...nel.org, linux-kernel@...r.kernel.org
Cc:	stable-review@...nel.org, Petr Tesarik <ptesarik@...e.cz>,
	Tony Luck <tony.luck@...el.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [34-longterm 140/260] Optimize ticket spinlocks in fsys_rt_sigprocmask

From: Petr Tesarik <ptesarik@...e.cz>

commit 2d2b6901649a62977452be85df53eda2412def24 upstream.

Tony's fix (f574c843191728d9407b766a027f779dcd27b272) has a small bug,
it incorrectly uses "r3" as a scratch register in the first of the two
unlock paths ... it is also inefficient.  Optimize the fast path again.

Signed-off-by: Petr Tesarik <ptesarik@...e.cz>
Signed-off-by: Tony Luck <tony.luck@...el.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 arch/ia64/kernel/fsys.S |   42 +++++++++++-------------------------------
 1 files changed, 11 insertions(+), 31 deletions(-)

diff --git a/arch/ia64/kernel/fsys.S b/arch/ia64/kernel/fsys.S
index 471a1e7..331d42b 100644
--- a/arch/ia64/kernel/fsys.S
+++ b/arch/ia64/kernel/fsys.S
@@ -420,34 +420,31 @@ EX(.fail_efault, ld8 r14=[r33])			// r14 <- *set
 	;;
 
 	RSM_PSR_I(p0, r18, r19)			// mask interrupt delivery
-	mov ar.ccv=0
 	andcm r14=r14,r17			// filter out SIGKILL & SIGSTOP
+	mov r8=EINVAL			// default to EINVAL
 
 #ifdef CONFIG_SMP
 	// __ticket_spin_trylock(r31)
 	ld4 r17=[r31]
-	mov r8=EINVAL			// default to EINVAL
-	;;
-	extr r9=r17,17,15
 	;;
-	xor r18=r17,r9
+	mov.m ar.ccv=r17
+	extr.u r9=r17,17,15
 	adds r19=1,r17
+	extr.u r18=r17,0,15
 	;;
-	extr.u r18=r18,0,15
+	cmp.eq p6,p7=r9,r18
 	;;
-	cmp.eq p0,p7=0,r18
+(p6)	cmpxchg4.acq r9=[r31],r19,ar.ccv
+(p6)	dep.z r20=r19,1,15		// next serving ticket for unlock
 (p7)	br.cond.spnt.many .lock_contention
-	mov.m ar.ccv=r17
-	;;
-	cmpxchg4.acq r9=[r31],r19,ar.ccv
 	;;
 	cmp4.eq p0,p7=r9,r17
+	adds r31=2,r31
 (p7)	br.cond.spnt.many .lock_contention
 	ld8 r3=[r2]			// re-read current->blocked now that we hold the lock
 	;;
 #else
 	ld8 r3=[r2]			// re-read current->blocked now that we hold the lock
-	mov r8=EINVAL			// default to EINVAL
 #endif
 	add r18=IA64_TASK_PENDING_OFFSET+IA64_SIGPENDING_SIGNAL_OFFSET,r16
 	add r19=IA64_TASK_SIGNAL_OFFSET,r16
@@ -503,16 +500,8 @@ EX(.fail_efault, ld8 r14=[r33])			// r14 <- *set
 
 #ifdef CONFIG_SMP
 	// __ticket_spin_unlock(r31)
-	adds r31=2,r31
-	;;
-	ld2.bias r2=[r31]
-	mov r3=65534
-	;;
-	adds r2=2,r2
-	;;
-	and r3=r3,r2
-	;;
-	st2.rel [r31]=r3
+	st2.rel [r31]=r20
+	mov r20=0					// i must not leak kernel bits...
 #endif
 	SSM_PSR_I(p0, p9, r31)
 	;;
@@ -535,16 +524,7 @@ EX(.fail_efault, (p15) st8 [r34]=r3)
 .sig_pending:
 #ifdef CONFIG_SMP
 	// __ticket_spin_unlock(r31)
-	adds r31=2,r31
-	;;
-	ld2.bias r2=[r31]
-	mov r3=65534
-	;;
-	adds r2=2,r2
-	;;
-	and r3=r3,r2
-	;;
-	st2.rel [r31]=r3
+	st2.rel [r31]=r20			// release the lock
 #endif
 	SSM_PSR_I(p0, p9, r17)
 	;;
-- 
1.7.3.3

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