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From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
npiggin@gmail.com, msuchanek@suse.de
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: [RFC PATCH v3 14/15] powerpc/syscall: Avoid stack frame in likely part of syscall_call_exception()
Date: Mon, 6 Apr 2020 18:16:50 +0000 (UTC) [thread overview]
Message-ID: <a5be904f44b273c67ac9c37cbed27dba9a34da6a.1586196948.git.christophe.leroy@c-s.fr> (raw)
In-Reply-To: <5aeaa33383e833f6eca30893fbd188b88e019eaa.1586196948.git.christophe.leroy@c-s.fr>
When r3 is not modified, reload it from regs->orig_r3 to free
volatile registers. This avoids a stack frame for the likely part
of syscall_call_exception()
Before : 353 cycles on null_syscall
After : 347 cycles on null_syscall
Before the patch:
c000b4d4 <system_call_exception>:
c000b4d4: 7c 08 02 a6 mflr r0
c000b4d8: 94 21 ff e0 stwu r1,-32(r1)
c000b4dc: 93 e1 00 1c stw r31,28(r1)
c000b4e0: 90 01 00 24 stw r0,36(r1)
c000b4e4: 90 6a 00 88 stw r3,136(r10)
c000b4e8: 81 6a 00 84 lwz r11,132(r10)
c000b4ec: 69 6b 00 02 xori r11,r11,2
c000b4f0: 55 6b ff fe rlwinm r11,r11,31,31,31
c000b4f4: 0f 0b 00 00 twnei r11,0
c000b4f8: 81 6a 00 a0 lwz r11,160(r10)
c000b4fc: 55 6b 07 fe clrlwi r11,r11,31
c000b500: 0f 0b 00 00 twnei r11,0
c000b504: 7c 0c 42 e6 mftb r0
c000b508: 83 e2 00 08 lwz r31,8(r2)
c000b50c: 81 82 00 28 lwz r12,40(r2)
c000b510: 90 02 00 24 stw r0,36(r2)
c000b514: 7d 8c f8 50 subf r12,r12,r31
c000b518: 7c 0c 02 14 add r0,r12,r0
c000b51c: 90 02 00 08 stw r0,8(r2)
c000b520: 7c 10 13 a6 mtspr 80,r0
c000b524: 81 62 00 70 lwz r11,112(r2)
c000b528: 71 60 86 91 andi. r0,r11,34449
c000b52c: 40 82 00 34 bne c000b560 <system_call_exception+0x8c>
c000b530: 2b 89 01 b6 cmplwi cr7,r9,438
c000b534: 41 9d 00 64 bgt cr7,c000b598 <system_call_exception+0xc4>
c000b538: 3d 40 c0 5c lis r10,-16292
c000b53c: 55 29 10 3a rlwinm r9,r9,2,0,29
c000b540: 39 4a 41 e8 addi r10,r10,16872
c000b544: 80 01 00 24 lwz r0,36(r1)
c000b548: 7d 2a 48 2e lwzx r9,r10,r9
c000b54c: 7c 08 03 a6 mtlr r0
c000b550: 7d 29 03 a6 mtctr r9
c000b554: 83 e1 00 1c lwz r31,28(r1)
c000b558: 38 21 00 20 addi r1,r1,32
c000b55c: 4e 80 04 20 bctr
After the patch:
c000b4d4 <system_call_exception>:
c000b4d4: 81 6a 00 84 lwz r11,132(r10)
c000b4d8: 90 6a 00 88 stw r3,136(r10)
c000b4dc: 69 6b 00 02 xori r11,r11,2
c000b4e0: 55 6b ff fe rlwinm r11,r11,31,31,31
c000b4e4: 0f 0b 00 00 twnei r11,0
c000b4e8: 80 6a 00 a0 lwz r3,160(r10)
c000b4ec: 54 63 07 fe clrlwi r3,r3,31
c000b4f0: 0f 03 00 00 twnei r3,0
c000b4f4: 7d 6c 42 e6 mftb r11
c000b4f8: 81 82 00 08 lwz r12,8(r2)
c000b4fc: 80 02 00 28 lwz r0,40(r2)
c000b500: 91 62 00 24 stw r11,36(r2)
c000b504: 7c 00 60 50 subf r0,r0,r12
c000b508: 7d 60 5a 14 add r11,r0,r11
c000b50c: 91 62 00 08 stw r11,8(r2)
c000b510: 7c 10 13 a6 mtspr 80,r0
c000b514: 80 62 00 70 lwz r3,112(r2)
c000b518: 70 6b 86 91 andi. r11,r3,34449
c000b51c: 40 82 00 28 bne c000b544 <system_call_exception+0x70>
c000b520: 2b 89 01 b6 cmplwi cr7,r9,438
c000b524: 41 9d 00 84 bgt cr7,c000b5a8 <system_call_exception+0xd4>
c000b528: 80 6a 00 88 lwz r3,136(r10)
c000b52c: 3d 40 c0 5c lis r10,-16292
c000b530: 55 29 10 3a rlwinm r9,r9,2,0,29
c000b534: 39 4a 41 e4 addi r10,r10,16868
c000b538: 7d 2a 48 2e lwzx r9,r10,r9
c000b53c: 7d 29 03 a6 mtctr r9
c000b540: 4e 80 04 20 bctr
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/kernel/syscall.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c
index f9fca9985b0f..af449a4a8e8f 100644
--- a/arch/powerpc/kernel/syscall.c
+++ b/arch/powerpc/kernel/syscall.c
@@ -85,6 +85,9 @@ notrace long system_call_exception(long r3, long r4, long r5,
} else if (unlikely(r0 >= NR_syscalls)) {
return -ENOSYS;
+ } else {
+ /* Restore r3 from orig_gpr3 to free up a volatile reg */
+ r3 = regs->orig_gpr3;
}
/* May be faster to do array_index_nospec? */
--
2.25.0
next prev parent reply other threads:[~2020-04-06 18:17 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-06 18:16 [RFC PATCH v3 01/15] powerpc/syscall: Refactorise from Nick Christophe Leroy
2020-04-06 18:16 ` [RFC PATCH v3 02/15] powerpc/radix: Make kuap_check_amr() and kuap_restore_amr() generic Christophe Leroy
2020-04-06 18:16 ` [RFC PATCH v3 03/15] powerpc/32s: Create C version of kuap_restore() and kuap_check() Christophe Leroy
2020-04-06 18:16 ` [RFC PATCH v3 04/15] powerpc/8xx: " Christophe Leroy
2020-04-06 18:16 ` [RFC PATCH v3 05/15] powerpc/irq: Add helpers to get and set regs->softe Christophe Leroy
2020-04-07 0:50 ` Nicholas Piggin
2020-04-06 18:16 ` [RFC PATCH v3 06/15] powerpc/irq: Add new helpers to play with MSR_EE and MSR_RI on PPC32 Christophe Leroy
2020-04-06 18:16 ` [RFC PATCH v3 07/15] powerpc/irq: Add stub irq_soft_mask_return() for PPC32 Christophe Leroy
2020-04-06 18:16 ` [RFC PATCH v3 08/15] powerpc/syscall: Rename syscall_64.c into syscall.c Christophe Leroy
2020-04-06 18:16 ` [RFC PATCH v3 09/15] powerpc/syscall: Make syscall_64.c buildable on PPC32 Christophe Leroy
2020-04-06 18:16 ` [RFC PATCH v3 10/15] powerpc/syscall: Use is_compat_task() Christophe Leroy
2020-04-06 18:16 ` [RFC PATCH v3 11/15] powerpc/syscall: Save r3 in regs->orig_r3 Christophe Leroy
2020-04-06 18:16 ` [RFC PATCH v3 12/15] powerpc/syscall: Selectively check MSR_RI and MSR_PR on syscall entry Christophe Leroy
2020-04-06 18:16 ` [RFC PATCH v3 13/15] powerpc/syscall: system call implement entry/exit logic in C for PPC32 Christophe Leroy
2020-04-06 18:16 ` Christophe Leroy [this message]
2020-04-06 18:16 ` [RFC PATCH v3 15/15] powerpc/kernel: Do not inconditionally save non volatile registers on system call Christophe Leroy
2020-04-07 1:10 ` Nicholas Piggin
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