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

[Jamie Lokier]

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),

Is this a timer that need to fire soon after setting, every time?

I wonder if a different kind of Windows timer, lower-resolution, could
be used if the timeout is longer.  If it has insufficient resolution,
it could be set to trigger a little early, then set a high-resolution
timer at that point.

Maybe that could help for Linux CONFIG_NOHZ guests?

-- Jamie