linux-kernel - Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall

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Date:	Tue, 21 Nov 2006 08:39:39 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Paul E. McKenney" <paulmck@...ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [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:
> 
> > > > 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.

That requires init_srcu_struct() to return the error. If it does that,
I'm fine with it.

> Does this answer your objection?  If not, can you explain in more detail 
> what other features you would like?

It does, if the allocation failure in init_srcu_struct() is signalled.

-- 
Jens Axboe

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