By "turning off Linux PGO testing", you really mean "stop making and distributing Linux PGO builds," right?
The main reason I'd want Linux PGO is for mobile. On desktop Linux, most users (I expect) don't run our builds, so it's not a big deal if they're some percent slower. (Unless distros commonly do PGO builds of Firefox?) But we're not doing mobile Linux PGO builds (that I know of), and I don't expect success with desktop PGO is much related to success with mobile PGO. -Justin On Wed, Oct 10, 2012 at 5:14 PM, David Anderson <bailo...@gmail.com> wrote: > Hi, > > After being faced with the prospect of debugging Yet Another PGO-only Bug, I > propose that we stop testing Linux PGO builds. One of these bugs is causing > perma-red on Aurora (bug 799295). The developer cost of figuring out how to > reproduce, debug, and fix these problems is quite high, and even higher where > a specific distro and compiler version might be in play. The cost is not > worth the benefit of testing this configuration. > > All evidence at Mozilla suggests that PGO is endlessly buggy, and I've heard > this has been true historically in compilers. PGO deeply and zealously > modifies calling conventions, function bodies, and large callgraphs, causing > subtle problems, often topcrashes, that are difficult to reproduce and nearly > impossible to debug. The result is that we litter the codebase with > untestable deoptimization hints that may or may not randomly become obsolete. > > This is depressing on any platform, but at least on Windows, we have a single > compiler version to worry about (and, notably, a compiler that has PGO bugs > even with a huge amount of resources behind its development). It is possible > that PGO could expose real bugs. If so, we'll see the bug one way or another, > likely in a context that is more easily reproducible and easier to debug. > > So, let's turn off Linux PGO testing, free up releng resources, and save > ourselves the inevitable pain and suffering. > > -David > _______________________________________________ > dev-platform mailing list > dev-platform@lists.mozilla.org > https://lists.mozilla.org/listinfo/dev-platform _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
