Messages in this thread | | | Date | Sat, 21 Jun 2008 14:02:03 -0400 | From | "Frank Ch. Eigler" <> | Subject | Re: [RFC][Patch 2/2] markers: example of irq regular kernel markers |
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Hi -
On Sat, Jun 21, 2008 at 06:13:54PM +0200, Peter Zijlstra wrote:
> [...] I think what Frank refers to here is why not scatter the > kernel code with trace_mark()s on every conceivable location like > you do with printk-style debugging.
It's not fair to caricaturize my suggestions this way ("every conceivable location").
> Those trace marks might help out when $customer's kernel goes splat > and you don't want to provide him with a custom kernel.
Right.
> I do think we must make a clear distinction between these cases because: > > 1) tracers provide a kernel<->user interface - and whilst we don't > have a stable in-kernel API/ABI we are anal about the kernel/user > boundary. Andrew also greatly worries about this aspect.
Well, how to set Andrew's mind at ease then, beyond what we've already said? Back a few months ago, both systemtap and lttng guys - the primary user-space clients - have said that we are fine with this interface changing. We each have mechanisms to adapt.
> 2) it highly uglyfies the code, Frank doesn't need to maintain it, > so its easy for him to say. But IMHO its much harder to read code > that is littered with debug statements that it is to read regular > code.
Then don't put too many in, or hide them with inline functions.
> 3) it bloats the kernel,.. while it may not be fast path bloat, all > that marker stuff does go somewhere.
That bloat has been quantified and appears negligible in space and time.
> So, while I see the value of 'stable' mark sites for 'stable' > events, I'm dead-set against littering the kernel with markers just > because we can, and hoping they might some day be useful for > someone.
We're in violent agreement. No one suggested "littering just because we can". The initial lttng suite of markers consisted of about one hundred *in total*. If some other subsystem maintainer runs amok and adds thousands, please take it up with them, not with us.
- FChE
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