Messages in this thread | | | Date | Mon, 29 Sep 2008 12:06:05 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH] LTTng relay buffer allocation, read, write |
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* Peter Zijlstra (a.p.zijlstra@chello.nl) wrote: > On Sat, 2008-09-27 at 19:10 +0200, Peter Zijlstra wrote: > > On Sat, 2008-09-27 at 09:40 -0400, Mathieu Desnoyers wrote: > > > > It does not provide _any_ sort of locking on buffer data. Locking should be done > > > by the caller. Given that we might think of very lightweight locking schemes, > > Which defeats the whole purpose of the exercise, we want to provide a > single mechanism - including locking - that is usable to all. Otherwise > everybody gets to do the hard part themselves, which will undoubtedly > result in many broken/suboptimal locking schemes. >
Well, this is my answer to Steven's "this is too complex" comments, which I suspect is really a "this is too implement to implement". Sorry Steven, but you do not actually propose anything to address my concerns, which are : I want to export this data to userspace without tricky dependencies on the compiler ABI. I also don't want to be limited in locking infrastructure implementation.
Those are the kind of concerns that are much easier to address in a layered and modular implementation. If we try to do everything in the same C file, we end up having typing/memory management/time management all closely tied.
So I am all for providing a common infrastructure which implements all this, but I think this infrastructure should itself be layered and modular.
Also, I have something really really near to the requirements expressed in LTTng, which is :
Linux Kernel Markers : Event data typing exportable to userspace without tricky compiler ABI dependency. TODO : Export marker list to debugfs. Allow individual marker enable/disable through debugfs file. Use per client buffer marker IDs rather than a global ID table. Export the markers IDs/format/name through one small buffer for each client buffer. ltt-relay : Buffer coherency management. TODO : splice. ltt-relay-alloc : Buffer allocation and read/write, without vmap. ltt-tracer : In-kernel API to manage trace allocation, start/stop. TODO : Currently has a statically limited set of buffers. Should be extended so that clients could register new buffers. ltt-control : Netlink control which calls the in-kernel ltt-tracer API. TODO : switch from netlink to debugfs. ltt-timestamp : Timestamping infrastructure (tsc, global counter). Currently supports about 6 architectures. Has an asm-generic fallback. ltt-heartbeat : Deal with 32 TSC overflow by periodically writing an event in every buffers. TODO : switch to "extended time" field by keeping track of the previously written timestamp.
If you think it's worthwhile, I could post a selected set of my patches to LKML to see the reactions. However, note that there are a few TODOs, so it does not address all the requirements.
Mathieu
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