From: Michael Ellerman Date: Wed, 25 Nov 2015 03:25:16 +0000 (+1100) Subject: powerpc/kernel: Drop HMT_MEDIUM_PPR_DISCARD X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=d6265aeaf815801ad53a95f11cea8ea752862176;p=openwrt%2Fstaging%2Fblogic.git 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 : 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 --- 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 @@ -129,15 +129,6 @@ BEGIN_FTR_SECTION_NESTED(941) \ mtspr SPRN_PPR,ra; \ 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 */ @@ -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)