Currently, when PMC is sampling call chains, it will sample a user-space call chain when the counter fires while in user space and will sample kernel-space call chains when the counter fires while in kernel space. This is useful functionality and should not be discarded.
However, there are cases where a user really wants to know the user-space call chain every time the sample counter fires, even if the sample counter fires while in kernel mode. This change adds this capability, which is activated when the user specifies an optional parameter.
(To go a step further, we discussed at BSDCan the fact that a user might like to be able to see both the kernel and user call chains associated with each sampling interval. However, this patch does not go that far.)
Note: This patch is against stable/10 + D4227 (diff 1). Once D4227 is committed, I will regenerate the patch against CURRENT. Until that time, this is probably more of a draft than a serious proposal.