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target-arm: Implement WFE as a yield operation

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Implement WFE to yield our timeslice to the next CPU.
This avoids slowdowns in multicore configurations caused
by one core busy-waiting on a spinlock which can't possibly
be unlocked until the other core has an opportunity to run.
This speeds up my test case A15 dual-core boot by a factor
of three (though it is still four or five times slower than
a single-core boot).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1393339545-22111-1-git-send-email-peter.maydell@linaro.org
Reviewed-by: Richard Henderson <rth@twiddle.net>
Tested-by: Rob Herring <rob.herring@linaro.org>
This commit is contained in:
Peter Maydell 2014-03-10 14:56:30 +00:00
parent 2b194951c5
commit 72c1d3af6e
5 changed files with 19 additions and 0 deletions
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1
include/exec/cpu-defs.h
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@ -59,6 +59,7 @@ typedef uint64_t target_ulong;
#define EXCP_HLT 0x10001 /* hlt instruction reached */
#define EXCP_DEBUG 0x10002 /* cpu stopped after a breakpoint or singlestep */
#define EXCP_HALTED 0x10003 /* cpu is halted (waiting for external event) */
#define EXCP_YIELD 0x10004 /* cpu wants to yield timeslice to another */
#define TB_JMP_CACHE_BITS 12
#define TB_JMP_CACHE_SIZE (1 << TB_JMP_CACHE_BITS)

1
target-arm/helper.h
View File

@ -50,6 +50,7 @@ DEF_HELPER_FLAGS_3(sel_flags, TCG_CALL_NO_RWG_SE,
i32, i32, i32, i32)
DEF_HELPER_2(exception, void, env, i32)
DEF_HELPER_1(wfi, void, env)
DEF_HELPER_1(wfe, void, env)
DEF_HELPER_3(cpsr_write, void, env, i32, i32)
DEF_HELPER_1(cpsr_read, i32, env)

9
target-arm/op_helper.c
View File

@ -225,6 +225,15 @@ void HELPER(wfi)(CPUARMState *env)
cpu_loop_exit(env);
}
void HELPER(wfe)(CPUARMState *env)
{
/* Don't actually halt the CPU, just yield back to top
* level loop
*/
env->exception_index = EXCP_YIELD;
cpu_loop_exit(env);
}
void HELPER(exception)(CPUARMState *env, uint32_t excp)
{
env->exception_index = excp;

6
target-arm/translate.c
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@ -3939,6 +3939,9 @@ static void gen_nop_hint(DisasContext *s, int val)
s->is_jmp = DISAS_WFI;
break;
case 2: /* wfe */
gen_set_pc_im(s, s->pc);
s->is_jmp = DISAS_WFE;
break;
case 4: /* sev */
case 5: /* sevl */
/* TODO: Implement SEV, SEVL and WFE. May help SMP performance. */
@ -10857,6 +10860,9 @@ static inline void gen_intermediate_code_internal(ARMCPU *cpu,
case DISAS_WFI:
gen_helper_wfi(cpu_env);
break;
case DISAS_WFE:
gen_helper_wfe(cpu_env);
break;
case DISAS_SWI:
gen_exception(EXCP_SWI);
break;

2
target-arm/translate.h
View File

@ -44,6 +44,8 @@ extern TCGv_ptr cpu_env;
* emitting unreachable code at the end of the TB in the A64 decoder
*/
#define DISAS_EXC 6
/* WFE */
#define DISAS_WFE 7
#ifdef TARGET_AARCH64
void a64_translate_init(void);