linux-kernel - RE: [patch 3/9] LTTng instrumentation tasklets

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Date:	Wed, 25 Mar 2009 06:52:32 -0700
From:	Chetan.Loke@...lex.Com
To:	<mingo@...e.hu>, <mathieu.desnoyers@...ymtl.ca>
CC:	<akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>,
	<ltt-dev@...ts.casi.polymtl.ca>, <fweisbec@...il.com>,
	<jbaron@...hat.com>, <peterz@...radead.org>, <tglx@...utronix.de>,
	<rmk+lkml@....linux.org.uk>, <mhiramat@...hat.com>,
	<fche@...hat.com>, <haoki@...hat.com>,
	<t-nishiie@...css.fujitsu.com>, <rostedt@...dmis.org>,
	<eduard.munteanu@...ux360.ro>
Subject: RE: [patch 3/9] LTTng instrumentation tasklets

 

> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org 
> [mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of Ingo Molnar
> Sent: Tuesday, March 24, 2009 1:56 PM
> To: Mathieu Desnoyers
> Cc: akpm@...ux-foundation.org; linux-kernel@...r.kernel.org; 
> ltt-dev@...ts.casi.polymtl.ca; Frederic Weisbecker; Jason 
> Baron; Peter Zijlstra; Thomas Gleixner; Russell King; Masami 
> Hiramatsu; Frank Ch. Eigler; Hideo AOKI; Takashi Nishiie; 
> Steven Rostedt; Eduard - Gabriel Munteanu
> Subject: Re: [patch 3/9] LTTng instrumentation tasklets
> 
> 
> * Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> 
> > tasklet entry and exit events.
> 
> > +DEFINE_TRACE(irq_tasklet_high_entry);
> > +DEFINE_TRACE(irq_tasklet_high_exit);
> > +DEFINE_TRACE(irq_tasklet_low_entry);
> > +DEFINE_TRACE(irq_tasklet_low_exit);
> 
> Dunno - tasklets are a legacy mechanism, not sure we want to 
> instrument them. 


Quick question. I understand this is unrelated to this patch. So I apologize in advance.
Ingo - you mentioned "tasklets are a legacy mechanism". Is there a plan to phase them out ? Let me draw a small picture as to what's bothering me.

With the SR-IOV support if there are 'N' virtual functions then there will be 'N' driver instances(actually N+1, 1 for the PF). If that driver drains the responses in the interrupt context then all such VF-instances could virtually block everyone else(because SR-IOV guys might also have MSI-X enabled).
So now all such drivers should alter their Rx path.Driver's can queue tasklets and can also get the performance they want.

Any suggestions?

thanks
Chetan--
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