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Subject: Re: [PATCH 2.6.27-rc5 resubmit] Fix itimer/many thread hang.
From: Frank Mayhar <fmayhar@google.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       Roland McGrath <roland@redhat.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       Alexey Dobriyan <adobriyan@gmail.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Oleg Nesterov <oleg@tv-sign.ru>
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Date: Thu, 18 Sep 2008 06:50:01 -0700
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On Thu, 2008-09-18 at 12:23 +0200, Ingo Molnar wrote:
> i'd not worry about those 160 bytes - getting this stuff to work fine is 
> far more important. Details around threading seem to be one of the 
> slowest converging technological details of Linux.

Okay, the next patch will have this simplification.

> a silly question:
> 
> > +#else /* CONFIG_SMP */
> > +
> > +/*
> > + * Allocate the thread_group_cputime structure appropriately for UP kernels
> > + * and fill in the current values of the fields.  Called from copy_signal()
> > + * via thread_group_cputime_clone_thread() when adding a second or subsequent
> > + * thread to a thread group.  Assumes interrupts are enabled when called.
> > + */
> > +int thread_group_cputime_alloc(struct task_struct *tsk)
> > +{
> 
> why is there _any_ assymetry needed between UP and SMP? These days we 
> just write straight code for SMP, and UP is just a single-CPU 
> special-case of it. _Sometimes_ if it's really worth it we do some UP 
> special cases but it's the exception, not the rule.

As far as I know, I still need to handle the SMP per_cpu allocate/free
differently from the UP kmalloc.  I'll check again, though; if that's no
longer the case, I'll fix it.
-- 
Frank Mayhar <fmayhar@google.com>
Google, Inc.