RE: [patch 3/9] LTTng instrumentation tasklets

Chetan.Loke
2009-03-25T13:52:52Z

> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org
> [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Ingo Molnar
> Sent: Tuesday, March 24, 2009 1:56 PM
> To: Mathieu Desnoyers
> Cc: akpm@linux-foundation.org; linux-kernel@vger.kernel.org;
> ltt-dev@lists.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@polymtl.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