linux-kernel - Re: [PATCH 2.6.27-rc5 resubmit] Fix itimer/many thread hang.

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Message-Id: <1221745801.5411.3.camel@bobble.smo.corp.google.com>
Date:	Thu, 18 Sep 2008 06:50:01 -0700
From:	Frank Mayhar <fmayhar@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Roland McGrath <roland@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...sign.ru>
Subject: Re: [PATCH 2.6.27-rc5 resubmit] Fix itimer/many thread hang.

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@...gle.com>
Google, Inc.

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