Messages in this thread | | | Date | Mon, 15 Oct 2018 17:09:03 +0200 | From | Sebastian Andrzej Siewior <> | Subject | Re: [PATCH] rcu: Use cpus_read_lock() while looking at cpu_online_mask |
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On 2018-10-15 23:07:15 [+0800], Boqun Feng wrote: > Hi, Sebastian Hi Boqun,
> On Mon, Oct 15, 2018 at 04:42:17PM +0200, Sebastian Andrzej Siewior wrote: > > On 2018-10-13 06:48:13 [-0700], Paul E. McKenney wrote: > > > > > > My concern would be that it would queue it by default for the current > > > CPU, which would serialize the processing, losing the concurrency of > > > grace-period initialization. But that was a long time ago, and perhaps > > > workqueues have changed. > > > > but the code here is always using the first CPU of a NUMA node or did I > > miss something? > > > > The thing is the original way is to pick one CPU for a *RCU* node to > run the grace-period work, but with your proposal, if a RCU node is > smaller than a NUMA node (having fewer CPUs), we could end up having two > grace-period works running on one CPU. I think that's Paul's concern.
Ah. Okay. From what I observed, the RCU nodes and NUMA nodes were 1:1 here. Noted. Given that I can enqueue a work item on an offlined CPU I don't see why commit fcc6354365015 ("rcu: Make expedited GPs handle CPU 0 being offline") should make a difference. Any objections to just revert it?
> Regards, > Boqun
Sebastian
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