Messages in this thread | | | Date | Sat, 15 Jan 2005 07:43:15 +0100 | From | Andi Kleen <> | Subject | Re: [PATCH] i386/x86-64: Fix timer SMP bootup race |
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On Fri, Jan 14, 2005 at 10:28:41PM -0800, Andrew Morton wrote: > Andi Kleen <ak@suse.de> wrote: > > > > This fixes a long standing race in 2.6 i386/x86-64 SMP boot. > > The per CPU timers would only get initialized after an secondary > > CPU was running. But during initialization the secondary CPU would > > already enable interrupts to compute the jiffies. When a per > > CPU timer fired in this window it would run into a BUG in timer.c > > because the timer heap for that CPU wasn't fully initialized. > > Why don't we just not call calibrate_delay() on the secondaries? It > doesn't seem to do anything. That way we can leave local interrupts > disabled.
It's used for the "accumulative bogomips". To quote Alan:
/* * Allow the user to impress friends. */
But taking it away doesn't help because the timer startup on the BP and the secondaries going into the idle loop isn't synchronized. You could add a synchronization step, but it would be far more complicated than fixing the ordering like I did.
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