RE: [patch 3/9] LTTng instrumentation tasklets

Chetan.Loke
2009-03-25T17:37:53Z

> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@infradead.org]
> Sent: Wednesday, March 25, 2009 10:18 AM
> To: Loke,Chetan
> Cc: mingo@elte.hu; mathieu.desnoyers@polymtl.ca;
> akpm@linux-foundation.org; linux-kernel@vger.kernel.org;
> ltt-dev@lists.casi.polymtl.ca; fweisbec@gmail.com;
> jbaron@redhat.com; tglx@linutronix.de;
> rmk+lkml@arm.linux.org.uk; mhiramat@redhat.com;
> fche@redhat.com; haoki@redhat.com;
> t-nishiie@np.css.fujitsu.com; rostedt@goodmis.org;
> eduard.munteanu@linux360.ro
> Subject: RE: [patch 3/9] LTTng instrumentation tasklets
>
> On Wed, 2009-03-25 at 06:52 -0700, Chetan.Loke@Emulex.Com wrote:
> > 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?
>
> Threaded interrupts?
>

If we truly need to address performance and scalability for the SCSI-subsystem then we need something lightweight.