Messages in this thread | | | Date | Fri, 25 Jan 2002 17:20:04 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [PATCH] syscall latency improvement #1 |
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On Fri, 25 Jan 2002, Andrew Morton wrote: > > > > Looking at the code, I suspect that 99.9% of this "improvement" comes from > > one thing, and one thing only: you removed the "cli" in the system call > > return path. > > Before the cli was in the stock kernel, I had added it in the > low-latency patch. Careful testing showed that it added > 13 machine cycles to a system call on a P3.
That sounds about right. The empty system call path is basically dominated by the trap/iret costs, and is on the order of 200 cycles or so on most CPU's. So 13 cycles would account for the roughly 5% improvement.
Linus
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