> OK, so I resurrected x86_64-mm-sched-clock-share.patch and
> x86_64-mm-sched-clock64.patch. The x86_64 box hangs on boot when using
> netconsole and printk timestamps too. Removing "time" from the kernel boot
> command line prevents that.
It's not worse than before for you CPU. The old code did
#ifndef CONFIG_NUMA
if (!cpu_khz || check_tsc_unstable())
#endif
/* no locking but a rare wrong value is not a big deal */
return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
So if it worked before it still will.
> This explains why the hang only happens with
> x86_64-mm-log-reason-why-tsc-was-marked-unstable.patch applied, too: that
> patch must be triggering a printk inside xtime_lock.
>
> Does someone want to cook up a lockless printk_clock() for i386 and x86_64?
With the fall back case changed back to jiffies sched_clock will be fully lockless.
-Andi
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