Messages in this thread | | | Subject | Re: [perfmon] Re: [perfmon2] perfmon2 merge news | From | Andi Kleen <> | Date | Wed, 14 Nov 2007 13:38:38 +0100 |
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Christoph Hellwig <hch@infradead.org> writes: > > I've done this a gazillion times before, so maybe instead of beeing a lazy > bastard you could look up mailinglist archive. It's not like this is the > first discussion of perfmon. But to get start look at the systems calls, > many of them are beasts like: > > int pfm_read_pmds(int fd, pfarg_pmd_t *pmds, int n) > > This is basically a read(2) (or for other syscalls a write) on something
At least for x86 and I suspect some 1other architectures we don't initially need a syscall at all for this. There is an instruction RDPMC who can read a performance counter just fine. It is also much faster and generally preferable for the case where a process measures events about itself. In fact it is essential for one of the use cases I would like to see perfmon used (replacement of RDTSC for cycle counting)
Later a syscall might be needed with event multiplexing, but that seems more like a far away non essential feature.
> else than the file descriptor provided to the system call. The right thing
I don't like read/write for this too much. I think it's better to have individual syscalls. After all that is CPU state and having syscalls for that does seem reasonable.
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