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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. Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Read the documentation in qemu-doc.html or on http://wiki.qemu.org - QEMU team