Messages in this thread |  | | Date | Mon, 20 Nov 2006 14:39:29 -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:
> On Mon, Nov 20 2006, Alan Stern wrote: > > Paul: > > > > Here's my version of your patch from yesterday. It's basically the same, > > but I cleaned up the code in a few places and fixed a bug (the sign of idx > > in srcu_read_unlock). Also I changed the init routine back to void, since > > it's no longer an error if the per-cpu allocation fails. > > > > More importantly, I added a static initializer and included the fast-path > > in synchronize_srcu. It's protected by the new symbol > > SMP__STORE_MB_LOAD_WORKS, which should be defined in arch-specific headers > > for those architectures where the store-mb-load pattern is safe. > > 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.
Alan
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