On Jun 23, 2011, at 2:03 PM, Alan Cox wrote: > On 6/23/2011 1:30 PM, Warner Losh wrote: >> On Jun 23, 2011, at 2:17 AM, Bjoern A. Zeeb wrote: >> >>> On Jun 23, 2011, at 5:24 AM, Alan Cox wrote: >>> >>>> Author: alc >>>> Date: Thu Jun 23 05:23:59 2011 >>>> New Revision: 223464 >>>> URL: http://svn.freebsd.org/changeset/base/223464 >>>> >>>> Log: >>>> Revert to using the page queues lock in vm_page_clear_dirty_mask() on >>>> MIPS. (At present, although atomic_clear_char() is defined by atomic.h >>>> on MIPS, it is not actually implemented by support.S.) >>> Thanks, >>> and good catch on the atomics even if not planned, just in time for 9.0:) >> Yea, there's some work there to fix them... Not sure we can even fix some >> of them atomically... >> > > I'm not sure that I understand what you mean by the second statement. Can > you elaborate? The 8- and 16-bit operations should be no less "atomic" than > the 32- and 64-bit operations. In general, regardless of the size of the > operation, the "sc" instruction may fail and the whole operation has to be > restarted if another processor (or I/O device) performs a concurrent, cache > coherent store to the same location (or even cache line) as the "ll" and "sc" > instructions are operating on. On the other hand, if the "sc" instruction > succeeds, whether you used it to change all of the 32 bits or just 8 of the > 32 bits, it should appear as an atomic change to any other processor.
I was thinking of the unaligned 16-bit case. Properly aligned I suppose is a requirement, so I retract my statement: those are easy to implement. Warner_______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
