On Tue, Oct 08, 2019 at 09:14:14AM -0500, Justin Hibbits wrote: > On Tue, 8 Oct 2019 11:16:04 +0300 > Konstantin Belousov <kostik...@gmail.com> wrote: > > > On Tue, Oct 08, 2019 at 01:36:34AM +0000, Justin Hibbits wrote: > > > Author: jhibbits > > > Date: Tue Oct 8 01:36:34 2019 > > > New Revision: 353296 > > > URL: https://svnweb.freebsd.org/changeset/base/353296 > > > > > > Log: > > > powerpc: Implement atomic_(f)cmpset_ for short and char > > > | > > > This adds two implementations for each atomic_fcmpset_ and > > > atomic_cmpset_ short and char functions, selectable at compile time > > > for the target architecture. By default, it uses a generic > > > shift-and-mask to perform atomic updates to sub-components of > > > 32-bit words from <sys/_atomic_subword.h>. However, if > > > ISA_206_ATOMICS is defined it uses the ll/sc instructions for > > > halfword and bytes, introduced in PowerISA 2.06. These > > > instructions are supported by all IBM processors from POWER7 on, as > > > well as the Freescale/NXP e6500 core. Although the e5500 and > > > e500mc both implement PowerISA 2.06 they do not implement these > > > instructions. As part of this, clean up the atomic_(f)cmpset_acq > > > and _rel wrappers, by using macros to reduce code duplication. > > > > > > ISA_206_ATOMICS requires clang or newer binutils (2.20 or later). > > > > > Why don't you use normal word-sized ll/sc tlwarx/stwcx, and only > > modifying the part of the register as needed ? This would work on > > all supported CPUs, right ? > > > > When kevans did the _atomic_subword.h, one of the arches involved was > > sparc64, which does not have ll/sc. Also for MIPS there are some fine > > details which might mean that C implementation is less work than using > > word-sized ll/sc. But why for power ? > > No real significant reason. In fact, the review's diff has exactly > what you're asking for. The only reason I modified it for commit with > Kyle's work was purely readability, I thought using the C wrapper with > atomic_fcmpset_() was just marginally cleaner. I haven't checked, but I > don't think the inline code difference is too great, but I'll have to do > another review of it to be sure. It's easy enough to commit the > original diff over top instead, if that's the better way to go.
If the generated code difference is not significant, it is a strong argument to keep the committed version. But I find it quite surprising. _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
