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Re: [Qemu-devel] [RFC 09/10] cpu: remove exit_request global.

From: Frederic Konrad
Subject: Re: [Qemu-devel] [RFC 09/10] cpu: remove exit_request global.
Date: Tue, 03 Feb 2015 10:37:56 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

On 29/01/2015 16:52, Peter Maydell wrote:
On 16 January 2015 at 17:19,  <address@hidden> wrote:
From: KONRAD Frederic <address@hidden>

This removes exit_request global and adds a variable in CPUState for this.
Only the flag for the first cpu is used for the moment as we are still with one
TCG thread.
--- a/cpus.c
+++ b/cpus.c
@@ -646,10 +646,14 @@ static void cpu_handle_guest_debug(CPUState *cpu)

  static void cpu_signal(int sig)
+    CPUState *cpu;
      if (current_cpu) {
-    exit_request = 1;
+    CPU_FOREACH(cpu) {
+        cpu->exit_loop_request = 1;
+    }
You can't do this -- this code is a signal handler so it could
get run at any time including while the list of CPUs is being
updated. (This is why we have the exit_request flag in the
first place rather than just setting the exit_request flag in
each CPU...)

Possibly you want exit_request to be a per-thread variable,
but I haven't thought much about it.

--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -249,6 +249,7 @@ struct CPUState {
      bool created;
      bool stop;
      bool stopped;
+    volatile sig_atomic_t exit_loop_request;
      volatile sig_atomic_t exit_request;
      uint32_t interrupt_request;
      int singlestep_enabled;
This would duplicate the exit_request and
exit_loop_request flags in the CPU, which is kind of odd.

-- PMM
Actually, what we want to do is remove exit_requested global because when it exits the loop in tcg_exec_all it does exit_requested = 0, and other vcpu doesn't exit.

This is not clear to me why we have both exit_requested global and exit_request in

Maybe we can just make exit_request thread local this might work.

Also, we need to be able to exit VCPU we want from a TCG thread.
eg: We want to flush all the tlb we need to exit all cpus but one..


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