Messages in this thread | | | Date | Tue, 20 Jan 2009 15:14:54 +0100 | From | Nick Piggin <> | Subject | Re: lmbench lat_mmap slowdown with CONFIG_PARAVIRT |
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On Tue, Jan 20, 2009 at 03:03:24PM +0100, Ingo Molnar wrote: > > * Ingo Molnar <mingo@elte.hu> wrote: > > > > Times I believe are in nanoseconds for lmbench, anyway lower is > > > better. > > > > > > non pv AVG=464.22 STD=5.56 > > > paravirt AVG=502.87 STD=7.36 > > > > > > Nearly 10% performance drop here, which is quite a bit... hopefully > > > people are testing the speed of their PV implementations against > > > non-PV bare metal :) > > > > Ouch, that looks unacceptably expensive. All the major distros turn > > CONFIG_PARAVIRT on. paravirt_ops was introduced in x86 with the express > > promise to have no measurable runtime overhead. > > Here are some more precise stats done via hw counters on a perfcounters > kernel using 'timec', running a modified version of the 'mmap performance > stress-test' app i made years ago. > > The MM benchmark app can be downloaded from: > > http://redhat.com/~mingo/misc/mmap-perf.c
BTW. the lmbench test I run directly (it's called lat_mmap.c, and gets compiled into a standalone lat_mmap exec by the standard lmbench build).
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