[ltt-dev] [patch 3/9] LTTng instrumentation tasklets

[Chetan.Loke at Emulex.Com]

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