Re: 9.4 broken on alpha

On Tue, Aug 25, 2015 at 06:09:17PM -0400, Tom Lane wrote:
> Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> > Tom Lane wrote:
> >> Well, strictly speaking, there were no uses of pg_read_barrier until 9.4.
> >> However, pg_write_barrier (which used "wmb") was in use since 9.2; so
> >> unless you're claiming your assembler knows wmb but not rmb, the code's
> >> failed to compile for Alpha since 9.2.
>
> > Actually according to this
> > http://www.cs.cmu.edu/afs/cs.cmu.edu/academic/class/15213-f98/doc/alpha-asm.pdf
> > there is a wmb instruction but there is no rmb.

Exactly, as I had explained in the Debian bug report [1] over a year
ago.

> Oh really? If rmb were a figment of someone's imagination, it would
> explain the build failure (although not why nobody's reported it till
> now).

I reported the failure to build on Alpha, with an explanation and a
patch to fix it, to the Debian package maintainers over a year ago,
and within about of a month of version 9.4 being uploaded to Debian.

My recollection is that prior versions (9.2 and 9.3) compiled on
Alpha so the use of the wrong barrier, and the fix, was in fact
reported in a timely fashion following the first reasonable chance to
observe the problem.

It has been built and running at Debian-Ports for over a year now as
I uploaded the fixed version to the Alpha unreleased distribution.

> It'd be easy enough to s/rmb/mb/ in 9.4 ... but not sure it's worth
> the trouble, since we're desupporting Alpha as of 9.5 anyway.

That is disappointing to hear. Why is that? It is still in use on
Alpha. What is the maintenance load for keeping the Alpha arch
specific code?

> If the effective desupport date is 9.4 instead,

It's not. The fixed and built 9.4 version was uploaded to Debian-Ports
Alpha (in the unreleased distribution) and has been in use for over a
year.

Regards,
Michael.

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=756368