Re: Integrate delay accounting with systemtap?

[Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>]

On Thu, Jul 12, 2007 at 10:34:31AM -0400, Frank Ch. Eigler wrote:
> Hi -
> 
> On Thu, Jul 12, 2007 at 07:59:23PM +0530, Ananth N Mavinakayanahalli wrote:
> 
> > > [...]  But systemtap scripts already run in kernel space.  How/why
> > > would you want them to talk across netlink sockets?
> 
> > See Documentation/accounting/getdelays.c
> 
> Yes, I see that, but this is exactly a user-space program using the
> netlink api to query the kernel.  This scenario does not apply to
> systemtap probes that run in kernel space.
> 
> > Given the data is available without any additional kernel
> > probe/hook, it would be good for SystemTap to do something similar
> > to getdelays.c
> 
> But the netlink widget is necessary primarly because user space has no
> access to the task struct with all the statistics fields in it.  A
> probe running in kernel space can access the task struct (more or
> less) directly.

Agreed. I was just thinking we should possibly not take a probe hit if
its not needed. I am fine as long as the information is available either
way.

Ananth