Messages in this thread |  | | Date | Mon, 20 Nov 2006 16:39:47 -0500 (EST) | From | Alan Stern <> | Subject | Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync |
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On Mon, 20 Nov 2006, Jens Axboe wrote:
> > > Must we introduce memory allocations in srcu_read_lock()? It makes it > > > much harder and nastier for me to use. I'd much prefer a failing > > > init_srcu(), seems like a much better API. > > > > Paul agrees with you that allocation failures in init_srcu() should be > > passed back to the caller, and I certainly don't mind doing so. > > > > However we can't remove the memory allocation in srcu_read_lock(). That > > was the point which started this whole thread: the per-cpu allocation > > cannot be done statically, and some users of a static SRCU structure can't > > easily call init_srcu() early enough. > > > > Once the allocation succeeds, the overhead in srcu_read_lock() is minimal. > > It's not about the overhead, it's about a potentially problematic > allocation.
I'm not sure what you mean by "problematic allocation". If you successfully call init_srcu_struct then the allocation will be taken care of. Later calls to srcu_read_lock won't experience any slowdowns or problems.
If your call to init_srcu_struct isn't successful then you have to decide how to handle it. You can ignore the failure and live with degraded performance (caused by cache-line contention and repeated attempts to do the per-cpu allocation), or you can give up entirely.
Does this answer your objection? If not, can you explain in more detail what other features you would like?
Alan Stern
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