On 12/11/2017 03:55 PM, Yury Norov wrote: > On Mon, Dec 11, 2017 at 03:35:02PM +0100, Christian Borntraeger wrote: >> >> >> On 12/11/2017 03:16 PM, Yury Norov wrote: >>> This benchmark sends many IPIs in different modes and measures >>> time for IPI delivery (first column), and total time, ie including >>> time to acknowledge the receive by sender (second column). >>> >>> The scenarios are: >>> Dry-run: do everything except actually sending IPI. Useful >>> to estimate system overhead. >>> Self-IPI: Send IPI to self CPU. >>> Normal IPI: Send IPI to some other CPU. >>> Broadcast IPI: Send broadcast IPI to all online CPUs. >>> >>> For virtualized guests, sending and reveiving IPIs causes guest exit. >>> I used this test to measure performance impact on KVM subsystem of >>> Christoffer Dall's series "Optimize KVM/ARM for VHE systems". >>> >>> https://www.spinics.net/lists/kvm/msg156755.html >>> >>> Test machine is ThunderX2, 112 online CPUs. Below the results normalized >>> to host dry-run time. Smaller - better. >>> >>> Host, v4.14: >>> Dry-run: 0 1 >>> Self-IPI: 9 18 >>> Normal IPI: 81 110 >>> Broadcast IPI: 0 2106 >>> >>> Guest, v4.14: >>> Dry-run: 0 1 >>> Self-IPI: 10 18 >>> Normal IPI: 305 525 >>> Broadcast IPI: 0 9729 >>> >>> Guest, v4.14 + VHE: >>> Dry-run: 0 1 >>> Self-IPI: 9 18 >>> Normal IPI: 176 343 >>> Broadcast IPI: 0 9885 [...] >>> +static int __init init_bench_ipi(void) >>> +{ >>> + ktime_t ipi, total; >>> + int ret; >>> + >>> + ret = bench_ipi(NTIMES, DRY_RUN, &ipi, &total); >>> + if (ret) >>> + pr_err("Dry-run FAILED: %d\n", ret); >>> + else >>> + pr_err("Dry-run: %18llu, %18llu ns\n", ipi, total); >> >> you do not use NTIMES here to calculate the average value. Is that intended? > > I think, it's more visually to represent all results in number of dry-run > times, like I did in patch description. So on kernel side I expose raw data > and calculate final values after finishing tests. I think it is highly confusing that the output from the patch description does not match the output from the real module. So can you make that match at least? > > If you think that average values are preferable, I can do that in v2. The raw numbers a propably fine, but then you might want to print the number of loop iterations in the output. If we want to do something fancy, we could do a combination of a smaller inner loop doing the test, then an outer loops redoing the inner loop and then you can do some min/max/average calculation. Not s
