Re: [RFC] Unified Ring Buffer (Next Generation)

[Andi Kleen <andi@firstfloor.org>]

> The plan here is to create a ring buffer that supports per-buffer instance
> "flags" that specify what must be supported: e.g. either splice() or mmap(),
> global vs per-cpu buffers, etc.

And you plan to test all those flags in the hot path? 

> The new implementation I propose lessens the complexity level, presents clear
> abstractions to deal with that complexity, and comes with a formal proof of
> correctness, all of which I think is really very important to give a good level
> of insurance that the ring buffer works as expected.

Any simplifcation for the ftrace buffer would be a good thing IMHO.

> > For debugging kernels etc. with tracing that's not that big an issue, but
> > I think it's a problem for "non debugging" use. After all Linux
> > still has the goal to be at least configurable as a low footprint operating
> > system.
> 
> My implementation, at the moment, has 50% less lines of code and is 25% smaller
> in object size than the current ring buffer.

Good.

> 
> But all in all, I think users needing _something_ to perform system-wide tracing
> shout a lot louder than users who need to save a few bytes. So let's try to get
> something good in first, while keeping an eye on the object size, and if it
> happens to be too large for some users, then they can always implement a
> slower and less efficient ring_buffer_tiny.c if they feel like it.

They don't need to, they already have kfifo.

> I totally agree with you. This is in good part why I spent a large part of 2009
> writing papers explaining my ring buffer, doing Promela models and formal proofs
> of correctness. I think after all that work, the abstractions I will use will be
> much easier to grap by anyone willing to do a bit of reading.

Writing papers is not a replacement for simple maintainable code.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.