On 10/05/2010 01:00 PM, rukhsana ansari wrote:
Hi, W.r.t: > Note that this is a tradeoff. If an idle core is available and the > scheduler places the iothread on that core, then the heavyweight exit is > replaced by a lightweight exit + IPI. If the iothread is co-located with > the vcpu, then we'll take a heavyweight exit in any case. > Q: Does the kvm kernel code check for such a condition and take a heavyweight exit?
No. The heavyweight exit is caused by a context switch (partial) or return to userspace (full).
> The first case is very likely if the host cpu is undercommitted and there is > heavy I/O activity. This is a typical subsystem benchmark scenario (as > opposed to a system benchmark like specvirt). My feeling is that total > system throughput will be decreased unless the scheduler is clever enough to > place the iothread and vcpu on the same host cpu when the system is > overcommitted. > > Q: Sorry if the answer is obvious here. If the heavyweight exit is taken when both threads are assigned to the same core, how will the system throughput increase?
Co-locating threads on the same core reduces cross-core traffic. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
