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tcg: remove global exit_request

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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: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Alex Bennée 2017-02-23 18:29:12 +00:00
parent 8d04fb55de
commit e5143e30fb
4 changed files with 18 additions and 26 deletions
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2
cpu-exec-common.c
View File

@ -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)
{

20
cpu-exec.c
View File

@ -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.

19
cpus.c
View File

@ -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();

3
include/exec/exec-all.h
View File

@ -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