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Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility
From: |
Theodore Tso |
Subject: |
Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility |
Date: |
Tue, 8 Nov 2011 05:41:33 -0500 |
On Nov 8, 2011, at 5:22 AM, Ingo Molnar wrote:
> We do even more than that, the perf ABI is fully backwards *and*
> forwards compatible: you can run older perf on newer ABIs and newer
> perf on older ABIs.
It's great to hear that! But in that case, there's an experiment we can't
really run, which is if perf had been developed in a separate tree, would it
have been just as successful?
My belief is that perf was successful because *you* and the other perf
developers were competent developers, and who got things right. Not because
it was inside the kernel tree. You've argued that things were much better
because it was inside the tree, but that's not actually something we can put to
a scientific repeatable experiment.
I will observe that some of the things that caused me to be come enraged by
system tap (such as the fact that I simply couldn't even build the damned thing
on a non-Red Hat compilation environment, would not have been solved by moving
Systemtap into the kernel git tree --- at least not without moving a large
number of its external dependencies into the kernel tree as well, such as the
elf library, et. al.) So there is a whole class of problems that were seen in
previous tooling systems that were not caused by the fact that they were
separate from the kernel, but that they weren't being developed by the kernel
developers, so they didn't understand how to make the tool work well for kernel
developers.
If we had gone back in time, and had the same set of perf developers working in
an external tree, and Systemtap and/or Oprofile had been developed in the
kernel tree, would it really have made that much difference? Sure, Linus and
other kernel developers would have yelled at the Systemtap and Oprofile folks
more, but I haven't seen that much evidence that they listened to us when they
were outside of the kernel tree, and it's not obvious they would have listened
with the code being inside the kernel tree.
My claim is that is that outcome wouldn't have been all that different, and
that's because the difference was *you*, Ingo Molnar, as a good engineer, would
have designed a good backwards compatible ABI whether the code was inside or
outside of the kernel, and you would have insisted on good taste and usefulness
to kernel programmers whether perf was in our out of the kernel, and you would
have insisted on kernel coding guidelines and regular release cycles, even if
perf was outside of the kernel. As Linus sometimes like to say, in many cases
it's more about the _people_.
Regards,
-- Ted
- Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels, (continued)
- Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels, Ted Ts'o, 2011/11/06
- Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels, Pekka Enberg, 2011/11/07
- Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels, Vince Weaver, 2011/11/07
- Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels, Ingo Molnar, 2011/11/07
- Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels, Frank Ch. Eigler, 2011/11/07
- Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels, Pekka Enberg, 2011/11/07
- Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels, Ted Ts'o, 2011/11/07
- [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility, Ingo Molnar, 2011/11/08
- Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility, Peter Zijlstra, 2011/11/08
- Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility, Ingo Molnar, 2011/11/08
- Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility,
Theodore Tso <=
- Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility, Pekka Enberg, 2011/11/08
- Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility, Theodore Tso, 2011/11/08
- Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility, Pekka Enberg, 2011/11/08
- Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility, Frank Ch. Eigler, 2011/11/08
- Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility, Pekka Enberg, 2011/11/08
- Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility, Ingo Molnar, 2011/11/08
- Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility, Peter Zijlstra, 2011/11/08
- Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility, Ingo Molnar, 2011/11/08
- Re: [Qemu-devel] [F.A.Q.] perf ABI backwards and forwards compatibility, Peter Zijlstra, 2011/11/09
- Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels, Vince Weaver, 2011/11/08