Commit e5143e30 authored by Alex Bennée's avatar Alex Bennée
Browse files

tcg: remove global exit_request 



There are now only two uses of the global exit_request left.

The first ensures we exit the run_loop when we first start to process
pending work and in the kick handler. This is just as easily done by
setting the first_cpu->exit_request flag.

The second use is in the round robin kick routine. The global
exit_request ensured every vCPU would set its local exit_request and
cause a full exit of the loop. Now the iothread isn't being held while
running we can just rely on the kick handler to push us out as intended.

We lightly re-factor the main vCPU thread to ensure cpu->exit_requests
cause us to exit the main loop and process any IO requests that might
come along. As an cpu->exit_request may legitimately get squashed
while processing the EXCP_INTERRUPT exception we also check
cpu->queued_work_first to ensure queued work is expedited as soon as
possible.

Signed-off-by: default avatarAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: default avatarRichard Henderson <rth@twiddle.net>
parent 8d04fb55

cpu-exec-common.c

+0 −2
Original line number Diff line number Diff line
@@ -23,8 +23,6 @@ 
#include "exec/exec-all.h"

#include "exec/memory-internal.h"



bool exit_request;



/* exit the current TB, but without causing any exception to be raised */

void cpu_loop_exit_noexc(CPUState *cpu)

{

cpu-exec.c

+7 −13
Original line number Diff line number Diff line
@@ -568,15 +568,13 @@ static inline void cpu_loop_exec_tb(CPUState *cpu, TranslationBlock *tb, 
    *tb_exit = ret & TB_EXIT_MASK;

    switch (*tb_exit) {

    case TB_EXIT_REQUESTED:

        /* Something asked us to stop executing

         * chained TBs; just continue round the main

         * loop. Whatever requested the exit will also

         * have set something else (eg exit_request or

         * interrupt_request) which we will handle

         * next time around the loop.  But we need to

         * ensure the zeroing of tcg_exit_req (see cpu_tb_exec)

         * comes before the next read of cpu->exit_request

         * or cpu->interrupt_request.

        /* Something asked us to stop executing chained TBs; just

         * continue round the main loop. Whatever requested the exit

         * will also have set something else (eg interrupt_request)

         * which we will handle next time around the loop.  But we

         * need to ensure the tcg_exit_req read in generated code

         * comes before the next read of cpu->exit_request or

         * cpu->interrupt_request.

         */

        smp_mb();

        *last_tb = NULL;
@@ -630,10 +628,6 @@ int cpu_exec(CPUState *cpu) 


    rcu_read_lock();



    if (unlikely(atomic_mb_read(&exit_request))) {

        cpu->exit_request = 1;

    }



    cc->cpu_exec_enter(cpu);



    /* Calculate difference between guest clock and host clock.

cpus.c

+11 −8
Original line number Diff line number Diff line
@@ -793,7 +793,6 @@ static inline int64_t qemu_tcg_next_kick(void) 
static void qemu_cpu_kick_rr_cpu(void)

{

    CPUState *cpu;

    atomic_mb_set(&exit_request, 1);

    do {

        cpu = atomic_mb_read(&tcg_current_rr_cpu);

        if (cpu) {
@@ -1316,11 +1315,11 @@ static void *qemu_tcg_cpu_thread_fn(void *arg) 


    start_tcg_kick_timer();



    /* process any pending work */

    atomic_mb_set(&exit_request, 1);



    cpu = first_cpu;



    /* process any pending work */

    cpu->exit_request = 1;



    while (1) {

        /* Account partial waits to QEMU_CLOCK_VIRTUAL.  */

        qemu_account_warp_timer();
@@ -1329,7 +1328,8 @@ static void *qemu_tcg_cpu_thread_fn(void *arg) 
            cpu = first_cpu;

        }



        for (; cpu != NULL && !exit_request; cpu = CPU_NEXT(cpu)) {

        while (cpu && !cpu->queued_work_first && !cpu->exit_request) {



            atomic_mb_set(&tcg_current_rr_cpu, cpu);



            qemu_clock_enable(QEMU_CLOCK_VIRTUAL,
@@ -1349,12 +1349,15 @@ static void *qemu_tcg_cpu_thread_fn(void *arg) 
                break;

            }



        } /* for cpu.. */

            cpu = CPU_NEXT(cpu);

        } /* while (cpu && !cpu->exit_request).. */



        /* Does not need atomic_mb_set because a spurious wakeup is okay.  */

        atomic_set(&tcg_current_rr_cpu, NULL);



        /* Pairs with smp_wmb in qemu_cpu_kick.  */

        atomic_mb_set(&exit_request, 0);

        if (cpu && cpu->exit_request) {

            atomic_mb_set(&cpu->exit_request, 0);

        }



        handle_icount_deadline();

include/exec/exec-all.h

+0 −3
Original line number Diff line number Diff line
@@ -404,7 +404,4 @@ bool memory_region_is_unassigned(MemoryRegion *mr); 
/* vl.c */

extern int singlestep;



/* cpu-exec.c, accessed with atomic_mb_read/atomic_mb_set */

extern bool exit_request;



#endif