Re: [Qemu-devel] [PATCH] main-loop: For tools, initialize timers as part of qemu_init_main_loop()

[Anthony Liguori <anthony@codemonkey.ws>]

On 01/21/2012 11:13 AM, Michael Roth wrote:
> In some cases initializing the alarm timers can lead to non-negligable
> overhead from programs that link against qemu-tool.o. At least,
> setting a max-resolution WinMM alarm timer via mm_start_timer() (the
> current default for Windows) can increase the "tick rate" on Windows
> OSs and affect frequency scaling, and in the case of tools that run
> in guest OSs such has qemu-ga, the impact can be fairly dramatic
> (+20%/20% user/sys time on a core 2 processor was observed from an idle
> Windows XP guest).
>
> This patch doesn't address the issue directly (not sure what a good
> solution would be for Windows, or what other situations it might be
> noticeable), but it at least limits the scope of the issue to programs
> that "opt-in" to using the main-loop.c functions by only enabling alarm
> timers when qemu_init_main_loop() is called, which is already required
> to make use of those facilities, so existing users shouldn't be
> affected.
>
> Signed-off-by: Michael Roth<mdroth@linux.vnet.ibm.com>

Applied.  Thanks.

Regards,

Anthony Liguori
> ---
>   main-loop.c |    2 +-
>   main-loop.h |   12 ++++++++++++
>   qemu-tool.c |    3 ++-
>   vl.c        |    5 +++++
>   4 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/main-loop.c b/main-loop.c
> index 62d95b9..db23de0 100644
> --- a/main-loop.c
> +++ b/main-loop.c
> @@ -199,7 +199,7 @@ static int qemu_signal_init(void)
>   }
>   #endif
>
> -int qemu_init_main_loop(void)
> +int main_loop_init(void)
>   {
>       int ret;
>
> diff --git a/main-loop.h b/main-loop.h
> index f971013..4987041 100644
> --- a/main-loop.h
> +++ b/main-loop.h
> @@ -41,10 +41,22 @@
>    * SIGUSR2, thread signals (SIGFPE, SIGILL, SIGSEGV, SIGBUS) and real-time
>    * signals if available.  Remember that Windows in practice does not have
>    * signals, though.
> + *
> + * In the case of QEMU tools, this will also start/initialize timers.
>    */
>   int qemu_init_main_loop(void);
>
>   /**
> + * main_loop_init: Initializes main loop
> + *
> + * Internal (but shared for compatibility reasons) initialization routine
> + * for the main loop. This should not be used by applications directly,
> + * use qemu_init_main_loop() instead.
> + *
> + */
> +int main_loop_init(void);
> +
> +/**
>    * main_loop_wait: Run one iteration of the main loop.
>    *
>    * If @nonblocking is true, poll for events, otherwise suspend until
> diff --git a/qemu-tool.c b/qemu-tool.c
> index 6b69668..183a583 100644
> --- a/qemu-tool.c
> +++ b/qemu-tool.c
> @@ -83,11 +83,12 @@ void qemu_clock_warp(QEMUClock *clock)
>   {
>   }
>
> -static void __attribute__((constructor)) init_main_loop(void)
> +int qemu_init_main_loop(void)
>   {
>       init_clocks();
>       init_timer_alarm();
>       qemu_clock_enable(vm_clock, false);
> +    return main_loop_init();
>   }
>
>   void slirp_select_fill(int *pnfds, fd_set *readfds,
> diff --git a/vl.c b/vl.c
> index ba55b35..74a47e6 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2136,6 +2136,11 @@ static void free_and_trace(gpointer mem)
>       free(mem);
>   }
>
> +int qemu_init_main_loop(void)
> +{
> +    return main_loop_init();
> +}
> +
>   int main(int argc, char **argv, char **envp)
>   {
>       const char *gdbstub_dev = NULL;