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authorMichael Ellerman <mpe@ellerman.id.au>2015-11-25 14:25:16 +1100
committerMichael Ellerman <mpe@ellerman.id.au>2015-12-17 22:40:57 +1100
commitd6265aeaf815801ad53a95f11cea8ea752862176 (patch)
treeccfd814e423b21069d19e0c6f8bdc3c8b8843693
parentcd5cdeb6c8a42fb87644b0eb5d240f6ce6172402 (diff)
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powerpc/kernel: Drop HMT_MEDIUM_PPR_DISCARD
HMT_MEDIUM_PPR_DISCARD is a macro which is present at the start of most of our first level exception handlers. It conditionally executes a HMT_MEDIUM instruction, which sets the processor priority to medium. On on modern systems, ie. Power7 and later, it is nop'ed out at boot. All it does is make the exception vectors more cramped, and consume 4 bytes of icache. On old systems it has the effect of boosting the processor priority at the start of exception processing. If we were previously in the idle loop for example, we may be at low or very low priority. This is desirable as we want to process the exception as fast as possible. However looking closely at the generated code, we see that in all cases we execute another HMT_MEDIUM just four instructions later. With code patching applied, the final code on an old (Power6) system will look like, eg: c000000000000300 <data_access_pSeries>: c000000000000300: 7c 42 13 78 mr r2,r2 <- c000000000000304: 7d b2 43 a6 mtsprg 2,r13 c000000000000308: 7d b1 42 a6 mfsprg r13,1 c00000000000030c: f9 2d 00 80 std r9,128(r13) c000000000000310: 60 00 00 00 nop c000000000000314: 7c 42 13 78 mr r2,r2 <- So I suggest that the added code complexity of HMT_MEDIUM_PPR_DISCARD is not justified by the benefit of boosting the processor priority for the duration of four instructions, and therefore we drop it. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
-rw-r--r--arch/powerpc/include/asm/exception-64s.h15
-rw-r--r--arch/powerpc/kernel/exceptions-64s.S9
2 files changed, 0 insertions, 24 deletions
diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 9ee10781121f..60b2bbda212d 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -130,15 +130,6 @@ BEGIN_FTR_SECTION_NESTED(941) \
END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,CPU_FTR_HAS_PPR,941)
/*
- * Increase the priority on systems where PPR save/restore is not
- * implemented/ supported.
- */
-#define HMT_MEDIUM_PPR_DISCARD \
-BEGIN_FTR_SECTION_NESTED(942) \
- HMT_MEDIUM; \
-END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,0,942) /*non P7*/
-
-/*
* Get an SPR into a register if the CPU has the given feature
*/
#define OPT_GET_SPR(ra, spr, ftr) \
@@ -346,7 +337,6 @@ do_kvm_##n: \
. = loc; \
.globl label##_pSeries; \
label##_pSeries: \
- HMT_MEDIUM_PPR_DISCARD; \
SET_SCRATCH0(r13); /* save r13 */ \
EXCEPTION_PROLOG_PSERIES(PACA_EXGEN, label##_common, \
EXC_STD, KVMTEST, vec)
@@ -362,7 +352,6 @@ label##_pSeries: \
. = loc; \
.globl label##_hv; \
label##_hv: \
- HMT_MEDIUM_PPR_DISCARD; \
SET_SCRATCH0(r13); /* save r13 */ \
EXCEPTION_PROLOG_PSERIES(PACA_EXGEN, label##_common, \
EXC_HV, KVMTEST, vec)
@@ -378,7 +367,6 @@ label##_hv: \
. = loc; \
.globl label##_relon_pSeries; \
label##_relon_pSeries: \
- HMT_MEDIUM_PPR_DISCARD; \
/* No guest interrupts come through here */ \
SET_SCRATCH0(r13); /* save r13 */ \
EXCEPTION_RELON_PROLOG_PSERIES(PACA_EXGEN, label##_common, \
@@ -394,7 +382,6 @@ label##_relon_pSeries: \
. = loc; \
.globl label##_relon_hv; \
label##_relon_hv: \
- HMT_MEDIUM_PPR_DISCARD; \
/* No guest interrupts come through here */ \
SET_SCRATCH0(r13); /* save r13 */ \
EXCEPTION_RELON_PROLOG_PSERIES(PACA_EXGEN, label##_common, \
@@ -448,7 +435,6 @@ label##_relon_hv: \
. = loc; \
.globl label##_pSeries; \
label##_pSeries: \
- HMT_MEDIUM_PPR_DISCARD; \
_MASKABLE_EXCEPTION_PSERIES(vec, label, \
EXC_STD, SOFTEN_TEST_PR)
@@ -466,7 +452,6 @@ label##_hv: \
EXCEPTION_PROLOG_PSERIES_1(label##_common, EXC_HV);
#define __MASKABLE_RELON_EXCEPTION_PSERIES(vec, label, h, extra) \
- HMT_MEDIUM_PPR_DISCARD; \
SET_SCRATCH0(r13); /* save r13 */ \
EXCEPTION_PROLOG_0(PACA_EXGEN); \
__EXCEPTION_PROLOG_1(PACA_EXGEN, extra, vec); \
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 3419cbf2ad59..0757f23d35aa 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -96,7 +96,6 @@ __start_interrupts:
.globl system_reset_pSeries;
system_reset_pSeries:
- HMT_MEDIUM_PPR_DISCARD
SET_SCRATCH0(r13)
#ifdef CONFIG_PPC_P7_NAP
BEGIN_FTR_SECTION
@@ -164,7 +163,6 @@ machine_check_pSeries_1:
* some code path might still want to branch into the original
* vector
*/
- HMT_MEDIUM_PPR_DISCARD
SET_SCRATCH0(r13) /* save r13 */
#ifdef CONFIG_PPC_P7_NAP
BEGIN_FTR_SECTION
@@ -199,7 +197,6 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE)
. = 0x300
.globl data_access_pSeries
data_access_pSeries:
- HMT_MEDIUM_PPR_DISCARD
SET_SCRATCH0(r13)
EXCEPTION_PROLOG_PSERIES(PACA_EXGEN, data_access_common, EXC_STD,
KVMTEST, 0x300)
@@ -207,7 +204,6 @@ data_access_pSeries:
. = 0x380
.globl data_access_slb_pSeries
data_access_slb_pSeries:
- HMT_MEDIUM_PPR_DISCARD
SET_SCRATCH0(r13)
EXCEPTION_PROLOG_0(PACA_EXSLB)
EXCEPTION_PROLOG_1(PACA_EXSLB, KVMTEST, 0x380)
@@ -239,7 +235,6 @@ data_access_slb_pSeries:
. = 0x480
.globl instruction_access_slb_pSeries
instruction_access_slb_pSeries:
- HMT_MEDIUM_PPR_DISCARD
SET_SCRATCH0(r13)
EXCEPTION_PROLOG_0(PACA_EXSLB)
EXCEPTION_PROLOG_1(PACA_EXSLB, KVMTEST, 0x480)
@@ -269,7 +264,6 @@ instruction_access_slb_pSeries:
.globl hardware_interrupt_hv;
hardware_interrupt_pSeries:
hardware_interrupt_hv:
- HMT_MEDIUM_PPR_DISCARD
BEGIN_FTR_SECTION
_MASKABLE_EXCEPTION_PSERIES(0x502, hardware_interrupt,
EXC_HV, SOFTEN_TEST_HV)
@@ -413,7 +407,6 @@ hv_facility_unavailable_trampoline:
. = 0x1500
.global denorm_exception_hv
denorm_exception_hv:
- HMT_MEDIUM_PPR_DISCARD
mtspr SPRN_SPRG_HSCRATCH0,r13
EXCEPTION_PROLOG_0(PACA_EXGEN)
EXCEPTION_PROLOG_1(PACA_EXGEN, NOTEST, 0x1500)
@@ -527,7 +520,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
machine_check_pSeries:
.globl machine_check_fwnmi
machine_check_fwnmi:
- HMT_MEDIUM_PPR_DISCARD
SET_SCRATCH0(r13) /* save r13 */
EXCEPTION_PROLOG_0(PACA_EXMC)
machine_check_pSeries_0:
@@ -711,7 +703,6 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE)
.globl system_reset_fwnmi
.align 7
system_reset_fwnmi:
- HMT_MEDIUM_PPR_DISCARD
SET_SCRATCH0(r13) /* save r13 */
EXCEPTION_PROLOG_PSERIES(PACA_EXGEN, system_reset_common, EXC_STD,
NOTEST, 0x100)