On 20.03.15 12:25, Paul Mackerras wrote: > On Fri, Mar 20, 2015 at 12:15:15PM +0100, Alexander Graf wrote: >> >> >> On 20.03.15 10:39, Paul Mackerras wrote: >>> This reads the timebase at various points in the real-mode guest >>> entry/exit code and uses that to accumulate total, minimum and >>> maximum time spent in those parts of the code. Currently these >>> times are accumulated per vcpu in 5 parts of the code: >>> >>> * rm_entry - time taken from the start of kvmppc_hv_entry() until >>> just before entering the guest. >>> * rm_intr - time from when we take a hypervisor interrupt in the >>> guest until we either re-enter the guest or decide to exit to the >>> host. This includes time spent handling hcalls in real mode. >>> * rm_exit - time from when we decide to exit the guest until the >>> return from kvmppc_hv_entry(). >>> * guest - time spend in the guest >>> * cede - time spent napping in real mode due to an H_CEDE hcall >>> while other threads in the same vcore are active. >>> >>> These times are exposed in debugfs in a directory per vcpu that >>> contains a file called "timings". This file contains one line for >>> each of the 5 timings above, with the name followed by a colon and >>> 4 numbers, which are the count (number of times the code has been >>> executed), the total time, the minimum time, and the maximum time, >>> all in nanoseconds. >>> >>> Signed-off-by: Paul Mackerras <paulus@xxxxxxxxx> >> >> Have you measure the additional overhead this brings? > > I haven't - in fact I did this patch so I could measure the overhead > or improvement from other changes I did, but it doesn't measure its > own overhead, of course. I guess I need a workload that does a > defined number of guest entries and exits and measure how fast it runs > with and without the patch (maybe something like H_SET_MODE in a > loop). I'll figure something out and post the results. Yeah, just measure the number of exits you can handle for a simple hcall. If there is measurable overhead, it's probably a good idea to move the statistics gathering into #ifdef paths for DEBUGFS or maybe even a separate EXIT_TIMING config option as we have it for booke. Alex -- 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
