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fe310: Split sched_run call from handle_trap

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This is a small optimization to the RISC-V trap handler. By splitting
the call to sched_run from the trap_handle call, loading the previous
thread ptr can be delayed until after it is determined that a schedule
run is required. This shaves of a few cycles during regular interrupts
that do not trigger the scheduler.
This commit is contained in:
Koen Zandberg 2020-08-27 21:15:18 +02:00
parent 4289b09a33
commit 1e5dc928ad
No known key found for this signature in database
GPG Key ID: 0895A893E6D2985B
1 changed files with 26 additions and 17 deletions
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43
cpu/fe310/irq_arch.c
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@ -97,9 +97,8 @@ void external_isr(void)
/**
* @brief Global trap and interrupt handler
*/
int handle_trap(unsigned int mcause)
void handle_trap(uint32_t mcause)
{
int res = 0;
/* Tell RIOT to set sched_context_switch_request instead of
* calling thread_yield(). */
fe310_in_isr = 1;
@ -134,22 +133,15 @@ int handle_trap(unsigned int mcause)
else {
#ifdef DEVELHELP
printf("Unhandled trap:\n");
printf(" mcause: 0x%08x\n", mcause);
printf(" mcause: 0x%"PRIx32"\n", mcause);
printf(" mepc: 0x%"PRIx32"\n", read_csr(mepc));
printf(" mtval: 0x%"PRIx32"\n", read_csr(mtval));
#endif
/* Unknown trap */
core_panic(PANIC_GENERAL_ERROR, "Unhandled trap");
}
/* Check if context change was requested */
if (sched_context_switch_request) {
res = sched_run();
}
/* ISR done - no more changes to thread states */
fe310_in_isr = 0;
return res;
}
/* Marking this as interrupt to ensure an mret at the end, provided by the
@ -180,23 +172,38 @@ static void __attribute((aligned(4))) __attribute__((interrupt)) trap_entry(void
"sw s0, "XTSTR(s0_OFFSET)"(sp) \n"
"sw s1, "XTSTR(s1_OFFSET)"(sp) \n"
/* Get the active thread (could be NULL) */
"lw s1, sched_active_thread \n"
/* Save the user stack ptr */
"mv s0, sp \n"
/* Load exception stack ptr */
"la sp, _sp \n"
/* Get the interrupt cause, PC and trap vector */
/* Get the interrupt cause */
"csrr a0, mcause \n"
/* Call trap handler, a0 contains the return value */
/* Call trap handler, a0 contains mcause before, and the return value after
* the call */
"call handle_trap \n"
/* Move stack pointer back */
/* Load the sched_context_switch_request */
"lw a0, sched_context_switch_request \n"
/* And skip the context switch if not requested */
"beqz a0, no_sched \n"
/* Get the previous active thread (could be NULL) */
"lw s1, sched_active_thread \n"
/* Run the scheduler */
"call sched_run \n"
"no_sched: \n"
/* Restore the thread stack pointer and check if a new thread must be
* scheduled */
"mv sp, s0 \n"
/* No context switch required, shortcut to restore */
/* No context switch required, shortcut to restore. a0 contains the return
* value of sched_run, or the sched_context_switch_request if the sched_run
* was skipped */
"beqz a0, no_switch \n"
/* Skips the rest of the save if no active thread */
@ -216,12 +223,14 @@ static void __attribute((aligned(4))) __attribute__((interrupt)) trap_entry(void
/* Grab mepc to save it to the stack */
"csrr s2, mepc \n"
/* Save return PC in stack frame */
"sw s2, "XTSTR(pc_OFFSET)"(sp) \n"
/* Save stack pointer of current thread */
"sw sp, "XTSTR(SP_OFFSET_IN_THREAD)"(s1) \n"
/* Context saving done, from here on the new thread is scheduled */
"null_thread: \n"
/* Get the new active thread (guaranteed to be non NULL) */