On 7/6/2022 1:05 PM, Florian Weimer wrote:
* Michael Catanzaro:
On Wed, Jul 6 2022 at 08:06:45 AM -0600, Jeff Law
<jeffreyalaw@xxxxxxxxx> wrote:
If I'm understanding things correctly, the original proposal is trying
to make a very special case of profiling work better -- a case that
99.9% of Fedora users do not need or care about. That seems like a
particularly bad cost/benefit for this proposal.
But all Fedora users benefit from performance improvements implemented
as a result of profiling.
I think we have no evidence that you could not get the same results
using Fedora's current profiling tools. If the GNOME's sysprof does not
work with Fedora, fix it or use something else. Do not change how
Fedora is built. It's not really going to work anyway because typical
workloads spent 5% to 10% in glibc's string functions. Those functions
won't have frame pointers without some non-trivial development work (and
also an ongoing maintenance cost). If you change compiler flags only,
you still won't get accurate backtraces in many cases.
Yea, it's not a complete solution.
I had some interactions with Red Hat's performance teams over the years,
and to my knowledge, the lack of frame pointers has never come up.
I had some discussions in this space with Peter Z (IIRC) when he was
still with Red Hat. We ran into a brick wall with the kernel insistence
on no dwarf unwinding and the performance impact of keeping frame
pointers around. This was the oprofile era IIRC, but the same
principles apply.
Jeff
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