On Thu, Dec 08, 2005 at 10:31:06PM +0300, Oleg Nesterov wrote:
> I can't see how this change can prevent idle cpus to be included in
> ->cpumask, cpu can add itself to nohz_cpu_mask right after some other
> cpu started new grace period.
Yes that can happen, but if they check for rcu_pending right after that
it will prevent them from going tickless atleast (which will prevent grace
periods from being unnecessarily extended). Something like below:
CPU0 CPU1
rcp->cur++; /* New GP */
smp_mb();
rsp->cpumask = 0x3
cpu_set(1, nohz_cpu_mask);
rcu_pending()?
- Yes,
cpu_clear(1, nohz_cpu_mask);
Abort going tickless
Ideally we would have needed a smp_mb() in CPU1 also between setting CPU1
in nohz_cpu_mask and checking for rcu_pending(), but I guess it is not needed
in s390 because of its strong ordering?
--
Thanks and Regards,
Srivatsa Vaddagiri,
Linux Technology Center,
IBM Software Labs,
Bangalore, INDIA - 560017
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