DragonFly BSD
DragonFly kernel List (threaded) for 2003-07
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Re: syscall messaging interface API

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Wed, 23 Jul 2003 14:32:30 -0700 (PDT)

: Didn't the L4 folks find a way to make system calls on Pentiums without using
:software interrupts?  Isn't this like 10x faster?
:I need to read stuff at the Pistachio site again but I think I am correct.
:Any chance that could get integrated into DflyBSD?  [sorry for shortenting :)]

    There are a number of ways to get into kernel mode.

    Call Gates -	Really slow
    Trap Gates -	Reasonable
    SYSENTER -		About twice as fast as a trap gate but there are
			issues (typical intel stupidity)

    Int0x80, 0x81, etc... those are trap gates.  Overhead on a 1GHz P3
    is about 100ns to get in and 100ns to get out.

    We are going to stick with trap gates for the foreseeable future.  There
    are plenty of other ways to make system calls more efficient in those
    situations that require it, like adding a feature to queue several
    system calls at once, or by chaining messages, etc...  99.9% of
    all programs ever written in the entire history of mankind would not
    have a noticeable improvement in performance so it just isn't worth
    worrying about.

					Matthew Dillon 

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