> I think the issue is the kernel is extremely concerned with the > efficiency of the syscall path. > > Very legitimately some benchmarks just measure that one path to see > how many thousands of syscalls per second can be made. > > To accelerate that path as much as possible, the linux kenel chooses > not to incur the overhead of preserving the FP registers on every > syscall. > > So kernel code that uses FP must first ensure any registers it uses > are preserved. I don't recall ever writing any FP kernel code, so I > don't know what facilities are available to do that. > > Greg >
Greg I had a vague idea about overhead being incurred due to the mode switch, but your clear explanation makes it a lot easier to understand _where_ this happens. It's very helpful, thank you for your response. Julie
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