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SubjectRe: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync
On Mon, Nov 20 2006, Alan Stern wrote:
> 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.

It's not about the overhead, it's about a potentially problematic
allocation.

--
Jens Axboe

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