On Mon, Jun 16, 2014 at 10:43:38PM +0530, Viresh Kumar wrote: > Cc'ing Mauro/Rafael/Srivatsa.. > > On Thu, Dec 12, 2013 at 7:38 PM, Peter Zijlstra <[email protected]> wrote: > > Use a ring-buffer like multi-version object structure which allows > > always having a coherent object; we use this to avoid having to > > disable IRQs while reading sched_clock() and avoids a problem when > > getting an NMI while changing the cyc2ns data. > > > > MAINLINE PRE POST > > > > sched_clock_stable: 1 1 1 > > (cold) sched_clock: 329841 331312 257223 > > (cold) local_clock: 301773 310296 309889 > > (warm) sched_clock: 38375 38247 25280 > > (warm) local_clock: 100371 102713 85268 > > (warm) rdtsc: 27340 27289 24247 > > sched_clock_stable: 0 0 0 > > (cold) sched_clock: 382634 372706 301224 > > (cold) local_clock: 396890 399275 399870 > > (warm) sched_clock: 38194 38124 25630 > > (warm) local_clock: 143452 148698 129629 > > (warm) rdtsc: 27345 27365 24307 > > > > Signed-off-by: Peter Zijlstra <[email protected]> > > --- > > arch/x86/include/asm/timer.h | 23 +++ > > arch/x86/kernel/cpu/perf_event.c | 14 +- > > arch/x86/kernel/tsc.c | 229 > > ++++++++++++++++++++++++++++++++++----- > > 3 files changed, 236 insertions(+), 30 deletions(-) > > Hi Peter, > > We have been following a bug around cpufreq changes in 3.14 > (https://bugzilla.kernel.org/show_bug.cgi?id=77201) and our tests > narrowed it down to this patch after which things aren't working > as expected.
> Mauro ([email protected]) have reported that since 3.14 > after doing hot-unplug/hotplug of CPU1, cpufreq POSTCHANGE notifications > for every second frequency change hangs his machine .. Ah, just a freeze? > Last working tag was: 3.13.8 and it started failing from 3.14 and fails > for latest 3.15 as well.. > > model name : AMD Turion(tm) 64 X2 Mobile Technology TL-64 > CPUFreq driver: powernow-k8 .. > CPUs: Only two CPUs, sharing clock line What's specific to this particular CPU? > Can you give any pointers, so that he can get it fixed ? So what you can try is force a cyc2ns read before the write in set_cyc2ns_scale(). I think its possible that if we do not do the read, the write will wait for a 'free' slot indefinitely.
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