Intel P6 vs P7 system call performance
On Mon, 16 Dec 2002, Linus Torvalds wrote [regarding vsyscall implementation]:
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The good news is that the kernel part really looks pretty clean.
Where is the CPU serializing instruction which must be executed before return to user mode, so that kernel accesses to hardware devices are guaranteed to complete before any subsequent user access begins? (Otherwise a read/write by the user to a memory-mapped device page can appear out-of-order with respect to the kernel accesses in a preceding syscall.) The only generally useful serializing instructions are IRET and CPUID; only IRET is implemented univerally.
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John Reiser, [email protected]