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Re: [Qemu-devel] [PATCH v8 2/9] icount: exit cpu loop on expire
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v8 2/9] icount: exit cpu loop on expire |
Date: |
Thu, 26 Jan 2017 14:02:45 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 |
On 26/01/2017 13:34, Pavel Dovgalyuk wrote:
> This patch adds check to break cpu loop when icount expires without
> setting the TB_EXIT_ICOUNT_EXPIRED flag. It happens when there is no
> available translated blocks and all instructions were executed.
> In icount replay mode unnecessary tb_find will be called (which may
> cause an exception) and execution will be non-deterministic.
>
> v8: refactored loop exit code and moved it to separate function
>
> Signed-off-by: Pavel Dovgalyuk <address@hidden>
> ---
> cpu-exec.c | 24 +++++++++++++++++++-----
> 1 file changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/cpu-exec.c b/cpu-exec.c
> index fa08c73..f9b8ec8 100644
> --- a/cpu-exec.c
> +++ b/cpu-exec.c
> @@ -523,9 +523,25 @@ static inline void cpu_handle_interrupt(CPUState *cpu,
> *last_tb = NULL;
> }
> }
> - if (unlikely(atomic_read(&cpu->exit_request) || replay_has_interrupt()))
> {
> +}
> +
> +
> +static void cpu_check_loop_exit(CPUState *cpu)
> +{
> + if (unlikely(atomic_read(&cpu->exit_request)
> + /* icount has expired, we need to break the execution loop.
> + This check is needed before tb_find to make execution
> + deterministic - tb_find may cause an exception
> + while translating the code from non-mapped page. */
> + || (use_icount && ((cpu->icount_extra == 0
> + && cpu->icount_decr.u16.low == 0)
> + || (int32_t)cpu->icount_decr.u32 < 0)))) {
Simpler:
use_icount &&
((int32_t)cpu->icount_decr.u32 < 0 ||
cpu->icount_decr.low + cpu->icount_extra == 0)
But I'm not sure that you need to test u32. After all you're not
testing tcg_exit_req, which is the equivalent when icount is disabled.
> atomic_set(&cpu->exit_request, 0);
> - cpu->exception_index = EXCP_INTERRUPT;
> + /* If there is an exception that wasn't replayed yet,
> + don't change exception_index. */
> + if (cpu->exception_index == -1) {
> + cpu->exception_index = EXCP_INTERRUPT;
> + }
> cpu_loop_exit(cpu);
The siglongjmp is effectively the same as exiting the for(;;) loop of
cpu_exec and going back to cpu_handle_exception. So I would just merge
this with cpu_handle_interrupt, which exits a lot with cpu_loop_exit too.
All cpu_loop_exit() calls in cpu_handle_interrupt become "return true",
similar to cpu_handle_exception, and then in cpu_exec you have:
/* if an exception is pending, we execute it here */
while (!cpu_handle_exception(cpu, &ret)) {
/* if an interrupt is pending, inject it and go back
* to cpu_handle_exception.
*/
while (!cpu_handle_interrupt(cpu, &last_tb)) {
tb = tb_find(cpu, last_tb, tb_exit);
cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit, &sc);
/* Try to align the host and virtual clocks
if the guest is in advance */
align_clocks(&sc, cpu);
}
}
break;
> #endif
> @@ -634,6 +647,7 @@ int cpu_exec(CPUState *cpu)
>
> for(;;) {
> cpu_handle_interrupt(cpu, &last_tb);
> + cpu_check_loop_exit(cpu);
if (cpu_should_check_exception_or_exit(cpu)) {
break;
}
> tb = tb_find(cpu, last_tb, tb_exit);
> cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit, &sc);
> /* Try to align the host and virtual clocks
>
>
>
- [Qemu-devel] [PATCH v8 0/9] replay additions, Pavel Dovgalyuk, 2017/01/26
- [Qemu-devel] [PATCH v8 1/9] replay: exception replay fix, Pavel Dovgalyuk, 2017/01/26
- [Qemu-devel] [PATCH v8 2/9] icount: exit cpu loop on expire, Pavel Dovgalyuk, 2017/01/26
- Re: [Qemu-devel] [PATCH v8 2/9] icount: exit cpu loop on expire,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH v8 2/9] icount: exit cpu loop on expire, Pavel Dovgalyuk, 2017/01/26
- Re: [Qemu-devel] [PATCH v8 2/9] icount: exit cpu loop on expire, Paolo Bonzini, 2017/01/26
- Re: [Qemu-devel] [PATCH v8 2/9] icount: exit cpu loop on expire, Pavel Dovgalyuk, 2017/01/26
- Re: [Qemu-devel] [PATCH v8 2/9] icount: exit cpu loop on expire, Paolo Bonzini, 2017/01/26
- Re: [Qemu-devel] [PATCH v8 2/9] icount: exit cpu loop on expire, Pavel Dovgalyuk, 2017/01/27
- Re: [Qemu-devel] [PATCH v8 2/9] icount: exit cpu loop on expire, Paolo Bonzini, 2017/01/27
[Qemu-devel] [PATCH v8 3/9] apic: save apic_delivered flag, Pavel Dovgalyuk, 2017/01/26