On Tue, Dec 17, 2019 at 7:48 AM Andrew Cooper <[email protected]> wrote: > > On 17/12/2019 14:40, Sergey Kovalev wrote: > > On break point event eight context switches occures. > > > > With fast single step it is possible to shorten path for two context > > switches > > and gain 35% spead-up. > > > > Was tested on Debian branch of Xen 4.12. See at: > > https://github.com/skvl/xen/tree/debian/knorrie/4.12/fast-singlestep > > > > Rebased on master: > > https://github.com/skvl/xen/tree/fast-singlestep > > > > Signed-off-by: Sergey Kovalev <[email protected]> > > 35% looks like a good number, but what is "fast single step"? All this > appears to be is plumbing for to cause an altp2m switch on single step.
Yes, a better explanation would be much needed here and I'm not 100% sure it correctly implements what I think it tries to. This is my interpretation of what the idea is: when using DRAKVUF (or another system using altp2m with shadow pages similar to what I describe in https://xenproject.org/2016/04/13/stealthy-monitoring-with-xen-altp2m), after a breakpoint is hit the system switches to the default unrestricted altp2m view with singlestep enabled. When the singlestep traps to Xen another vm_event is sent to the monitor agent, which then normally disables singlestepping and switches the altp2m view back to the restricted view. This patch looks like its short-circuiting that last part so that it doesn't need to send the vm_event out for the singlestep event and should switch back to the restricted view in Xen automatically. It's a nice optimization. But what seems to be missing is the altp2m switch itself. Tamas _______________________________________________ Xen-devel mailing list [email protected] https://lists.xenproject.org/mailman/listinfo/xen-devel
