Messages in this thread | | | Date | Tue, 20 Aug 2019 13:31:35 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 1/1] Fix: trace sched switch start/stop racy updates |
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On Tue, Aug 20, 2019 at 04:01:16PM +0200, Peter Zijlstra wrote: > On Fri, Aug 16, 2019 at 09:52:17PM -0700, Paul E. McKenney wrote: > > On Fri, Aug 16, 2019 at 03:57:43PM -0700, Linus Torvalds wrote: > > > > [ . . . ] > > > > > We add READ_ONCE and WRITE_ONCE annotations when they make sense. Not > > > because of some theoretical "compiler is free to do garbage" > > > arguments. If such garbage happens, we need to fix the compiler, the > > > same way we already do with > > > > > > -fno-strict-aliasing > > > > Yeah, the compete-with-FORTRAN stuff. :-/ > > > > There is some work going on in the C committee on this, where the > > theorists would like to restrict strict-alias based optimizations to > > enable better analysis tooling. And no, although the theorists are > > pushing in the direction we would like them to, as far as I can see > > they are not pushing as far as we would like. But it might be that > > -fno-strict-aliasing needs some upgrades as well. I expect to learn > > more at the next meeting in a few months. > > > > http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2364.pdf > > http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2363.pdf > > http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2362.pdf > > We really should get the compiler folks to give us a > -fno-pointer-provenance. Waiting on the standards committee to get their > act together seems unlikely, esp. given that some people actually seem > to _want_ this nonsense :/
The reason that they want it is to enable some significant optimizations in numerical code on the one hand and in heavily templated C++ code on the other. Neither of which has much bearing on kernel code.
Interested in coming to the next C standards committee meeting in October to help me push for this? ;-)
Thanx, Paul
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