Messages in this thread |  | | | Subject | Re: [PATCH 1/5] ftrace: Synchronize variable setting with breakpoints | | From | Peter Zijlstra <> | | Date | Thu, 31 May 2012 21:06:16 +0200 |
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On Thu, 2012-05-31 at 14:50 -0400, Steven Rostedt wrote:
> > Well, the fail is before that, how could we grow two pieces of code > > doing similar things in the first place? > > Again, ftrace is slightly different as it does 30,000 changes at once, > on top of known nops. This was done through stop_machine(), thus any > slowdown was a large hit to system performance. text_poke() took the way > of mapping a page to do the change, and Mathieu didn't want to change > that (IIRC). But now we want the two to be similar.
We could give text_poke a function argument to do the actual modification, leaving all the magic centralized.
Also, why did Mathieu insist on keeping that kmap()?
> > I hardly ever use dyn-ftrace but I do use some text_poke() through > > jump_labels. > > You don't use function tracer? That's dyn-ftrace.
Not much no.. I do use trace_printk() and ftrace_dump_on_oops a lot though.
> But still, we need to keep the record as small as possible because it is > persistent throughout the life of the system running. Every location > must be recorded, and maintain a state (flags). > > Text_poke() mostly grew out of the jump-label work. But yes, there's > still a lot that can be shared. The actual code modification may be.
Afaicr we didn't change text_poke() for the jump-label stuff, except in trivial ways (added a #ifdef and exposed a function etc..).
> > I would still like to end up with one code base doing CMC with two > > implementations depending on a Kconfig knob. > > You mean keep stop_machine around?
Yeah, like have CONFIG_CMC_STOPMACHINE and CONFIG_CMC_FANCY for a little while.
If we find a problem with the fancy approach going back is easy, once its proven stable we could remove the stop-machine one.
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