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Linus Torvalds wrote: > > However, you also say: > >> It is advantageous for user space to use the register the kernel >> typically won't, in order to speed up system call entry/exit. > > but I'm not seeing the reason for that one. Care to comment more? (Yes, > there is often a latency from segment reload to use, but the reload > latency for system call exit *should* be entirely covered by the cost of > doing the system call return itself, no?) > I do seem to recall that some processor implementations can load a NULL segment faster than a non-NULL segment. This was significant enough that we wanted to use %fs in x86-64 userspace, as opposed to the original ABI which used %gs both in userspace and in the kernel. -hpa - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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