472711 - why do PGO dep builds take so long?

Status: RESOLVED INCOMPLETE

(Firefox Build System :: General, defect)

Description

[(not currently active) Ted Mielczarek]

I did a PGO clobber build this morning:
real    90m25.266s

then later I did a PGO dep build:
real    92m46.109s

It took 2 minutes *longer* than the clobber! I don't know why. My only possible theory is that the .pgd file contains the profiling info from the first run, so the re-links in the dep build take longer.

Comment 1

[(not currently active) Ted Mielczarek]

Here's a build log from my dep build, if anyone wants to sanity-check:
http://people.mozilla.com/~tmielczarek/pgo-build.log.bz2

Comment 2

[[e-mail] (:bhearsum)]

Here's a quick, completely unscientific survey of nightly build times on 1.9.1/1.9.2:
3h30min, 3h50min, 4h25min, 4h, 2h50min, 3h45min, 3h45min, 4h10min
Note that this is for the full build process, not just the "compile" step

Here's the same thing for dep builds:
2h50min, 2h45min, 3h10min, 2h55min, 1h40min (wow), 3h15min, 2h30min

As you can see, dep builds are certainly quicker but there's a lot of disparity within each set.

Comment 3

[(not currently active) Ted Mielczarek]

This might have been changed by bug 518107.

Comment 4

[Gregory Szorc [:gps]]

I don't see a compelling reason to keep this bug open.