Talk:IF (x86 flag)

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[edit] CLI a memory barrier?

I looked through the Intel manuals searching for this information, and I cannot find a truly definitive answer. In chapter 7, volume 3 of the manual, it has information on memory ordering and serializing instructions, in which CLI is not listed as a memory barrier or a serializing instruction. I am not claiming that CLI is not a membar; in fact, intuition would tell me that it is. However, I'd like to get a definitive answer before we put this sort of information up on the page. http://www.intel.com/design/pentium4/manuals/index_new.htm

Be sure to also look up the effects of changing the EFLAGS register. I may be simply miss-remembering what the effect really was. Jsmethers 06:21, 23 December 2005 (UTC)

It may have been that chaging the IF flag in the EFLAGS register caused the processor to synchronize the instruction stream, and thus more or less made CLI and STI slow operations. Jsmethers 06:24, 23 December 2005 (UTC)

Neither CLI or STI are memory barriers since they are not listed in that table in the manual. There is no reason for them to be, although of course implementations may chose to make them serializing. I'm removing the incorrect statement from this page. David.kaplan 04:38, 3 May 2007 (UTC)