Re: [tip:perf/core] tools/perf: Add required memory barriers

From: Ingo Molnar
Date: Thu Nov 07 2013 - 03:21:36 EST

* Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> > Requiring the user of a kernel interface to have a deep knowledge of
> > optimizing compilers, barriers, and CPU memory models is just asking
> > for trouble.
> It shouldn't be all that hard to put this in a (lgpl) library others can
> link to -- that way you can build it once (using GCC).

I'd suggest to expose it via a new perf syscall, using vsyscall methods to
not have to enter the kernel for the pure user-space bits. It should also
have a real usecase in tools/perf/ so that it's constantly tested, with
matching 'perf test' entries, etc.

I don't want a library that is external and under-tested: for example
quite a few of the PAPI breakages were found very late, after a new kernel
has been released - that's the big disadvantage of librarization and
decentralization. The decentralized library model might work if all you
want to create is a second-class also-ran GUI, but it just doesn't work
very well for actively developed kernel code.


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