On 7/6/2022 7:26 AM, Marek Polacek wrote:
On Tue, Jul 05, 2022 at 03:47:26PM -0400, Matthias Clasen wrote:
On Tue, Jul 5, 2022 at 3:40 PM Marek Polacek <polacek@xxxxxxxxxx> wrote:
Maybe not, but even ~1% is still an unacceptable slowdown. It would take
about a year for the compiler to catch up.
(Un)acceptable for whom?
GCC maintainers in Fedora, at least.
And why would it be unacceptable?
Because it's too much.
You just said compilers will make up for it quickly, not to mention
hardware continuously getting faster too...
Dozens of developers working a whole release (if not more) is not quick.
I haven't seen any convincing arguments as to why such a small
drop would be the end of the world.
And likewise, I haven't seen how this proposal would be helpful to the
majority of users, nevermind that it'd likely break programs using
inline assembly that use %rbp. But others have already raised similar
points in this thread.
And I don't think Fedora is or should be used in high-speed trading or
similar
environments where every microsecond matters.
I think you may be underestimating how much even 1% matters.
Amen. A 1% hit is very significant -- as Marek indicated, that's
roughly a year of work for the GCC community to recover.
Sometimes we're willing to take a 1% hit, sometimes not. It's a
question of balancing the performance hit against the benefits of
whatever change is being considered.
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.
Jeff
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