On Mon, Oct 26, 2015 at 11:20:01AM +0900, Michael Ellerman wrote: > > Sorry guys, these threads are so long I tend not to read them very actively :} > > Looking at the system call path, the straight line path does not include any > barriers. I can't see any hidden in macros either. > > We also have an explicit sync in the switch_to() path, which suggests that we > know system call is not a full barrier. > > Also looking at the architecture, section 1.5 which talks about the > synchronisation that occurs on system calls, defines nothing in terms of > memory ordering, and includes a programming note which says "Unlike the > Synchronize instruction, a context synchronizing operation does not affect the > order in which storage accesses are performed.". > Thank you, Michael. So IIUC, "sc" and "rfid" just imply an execution barrier like "isync" rather than a memory barrier. So memory barriers are needed if a system call need a memory ordering guarantee. Regards, Boqun > Whether that's actually how it's implemented I don't know, I'll see if I can > find out. > > cheers >
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