linux-kernel - Re: [PATCH 1/2] RT: Preemptible Function-Call-IPI Support

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Message-ID: <20070731092119.GA15968@elte.hu>
Date:	Tue, 31 Jul 2007 11:21:19 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Gregory Haskins <ghaskins@...ell.com>
Cc:	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] RT: Preemptible Function-Call-IPI Support

[ mail re-sent with lkml Cc:-ed. _Please_ Cc: all patches to lkml too! 
  Unless you want -rt to suffer the fate of -ck, keep upstream involved 
  all the time. The recent /proc/interrupts-all discussion with upstream 
  folks showed the clear benefits of that approach. ]

* Gregory Haskins <ghaskins@...ell.com> wrote:

> This code allows FUNCTION_CALL IPIs to become preemptible by executing 
> them in kthread context instead of interrupt context.  They are 
> referred to as "Virtual Function Call IPIs" (VFCIPI) because we no 
> longer rely on the actual FCIPI facility.  Instead we schedule a 
> thread to run.  This essentially replaces the synchronous FCIPI with 
> an async RESCHEDULE IPI.

why do we need this? It's quite complex and brings little extra AFAICS. 
See the "schedule_on_each_cpu-enhance.patch" from Peter Ziljstra that 
lets a function to be executed on all CPUs. That should be extended 
(trivially) to execute a function on another CPU. That's all we need. 

	Ingo
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