Am 25.02.2013 20:07, schrieb Alex Barcelo: > I'm struggling with the code to understand the "duty and soul" of the > "qemu_cpu_is_self" function (@cpus.c), and I quite not get it. > > I see that this function is called from some points. E.g., from > tcg_hangle_interrupt and run_on_cpu. Amongst others. > > Sometimes, seems to me that this function duty is "returns if the > actual thread is an VCPU thread" and sometimes the duty is "return if > the actual thread is specifically this VCPU thread". > > On non-KVM QEMU vanilla, this makes no difference because of a unique > VCPU thread. But imagine that there is an emulation thread which > controls multiple VCPU threads... > > ... then I'm stuck. Somebody can enlighten me? The in-code comments > don't help me anymore, and I'm a little thick following the code > logic.
Quite simply, TCG is not multi-threaded except for NPTL today. (And at least some such linux-user use cases are known broken.) Xen and qtest don't actually use the CPU AFAIK. The function should give you two hints, "self" and CPUState *cpu. The implementation further checks against a per-CPUState variable. So if you are changing TCG code to multi-threaded and run into wrong assumptions there, then you will need to fix them. According to my own commit message there was a qemu_in_vcpu_thread() function introduced ~Q2 2012. Regards, Andreas http://git.qemu.org/?p=qemu.git;a=commit;h=b7680cb6078bd7294a3dd86473d3f2fdee991dd0 http://git.qemu.org/?p=qemu.git;a=commit;h=60e82579c75068cb49af95595aa99d727e657a0a -- SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg
