From: Helge Deller <deller@gmx.de>
To: linux-parisc@vger.kernel.org,
James Bottomley <James.Bottomley@hansenpartnership.com>,
John David Anglin <dave.anglin@bell.net>
Subject: [PATCH] parisc: Drop LDCW barrier in CAS code when running UP
Date: Tue, 7 May 2019 20:19:05 +0200 [thread overview]
Message-ID: <20190507181905.GA16683@ls3530.dellerweb.de> (raw)
When running an SMP kernel on a single-CPU machine, we can speed up the
CAS code by replacing the LDCW sync barrier with NOP.
Signed-off-by: Helge Deller <deller@gmx.de>
diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
index e54d5e4d3489..97ac707c6bff 100644
--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -641,7 +641,8 @@ cas_action:
2: stw %r24, 0(%r26)
/* Free lock */
#ifdef CONFIG_SMP
- LDCW 0(%sr2,%r20), %r1 /* Barrier */
+98: LDCW 0(%sr2,%r20), %r1 /* Barrier */
+99: ALTERNATIVE(98b, 99b, ALT_COND_NO_SMP, INSN_NOP)
#endif
stw %r20, 0(%sr2,%r20)
#if ENABLE_LWS_DEBUG
@@ -658,7 +659,8 @@ cas_action:
/* Error occurred on load or store */
/* Free lock */
#ifdef CONFIG_SMP
- LDCW 0(%sr2,%r20), %r1 /* Barrier */
+98: LDCW 0(%sr2,%r20), %r1 /* Barrier */
+99: ALTERNATIVE(98b, 99b, ALT_COND_NO_SMP, INSN_NOP)
#endif
stw %r20, 0(%sr2,%r20)
#if ENABLE_LWS_DEBUG
@@ -862,7 +864,8 @@ cas2_action:
cas2_end:
/* Free lock */
#ifdef CONFIG_SMP
- LDCW 0(%sr2,%r20), %r1 /* Barrier */
+98: LDCW 0(%sr2,%r20), %r1 /* Barrier */
+99: ALTERNATIVE(98b, 99b, ALT_COND_NO_SMP, INSN_NOP)
#endif
stw %r20, 0(%sr2,%r20)
/* Enable interrupts */
@@ -875,7 +878,8 @@ cas2_end:
/* Error occurred on load or store */
/* Free lock */
#ifdef CONFIG_SMP
- LDCW 0(%sr2,%r20), %r1 /* Barrier */
+98: LDCW 0(%sr2,%r20), %r1 /* Barrier */
+99: ALTERNATIVE(98b, 99b, ALT_COND_NO_SMP, INSN_NOP)
#endif
stw %r20, 0(%sr2,%r20)
ssm PSW_SM_I, %r0
reply other threads:[~2019-05-07 18:19 UTC|newest]
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