Message-ID: <1040255473.3e0109f183d7e@209.51.155.18>
Date: Wed, 18 Dec 2002 18:51:13 -0500
From: billyrose@billyrose.net
To: root@chaos.analogic.com
Cc: linux-kernel@vger.kernel.org
Subject: Re: Intel P6 vs P7 system call performance
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Richard B. Johnson wrote:
> The number of CPU clocks necessary to make the 'far' or
> full-pointer call by pushing the segment register, the offset,
> then issuing a 'lret' is 33 clocks on a Pentium II.
>
> longcall clocks = 46
> call clocks = 13
> actual full-pointer call clocks = 33

this is not correct. the assumed target (of a _far_ call) would issue a far 
return and only an offset would be left on the stack to return to (oops). the 
code segment of the orginal caller needs pushed to create the seg:off pair and 
hence a far return would land back at the original calling routine. this is a 
very convoluted method of making the orginal call being far, as simply calling 
far in the first pace should issue much faster. OTOH, if you are making a 
workaround to an already existing piece of code, this works beautifully (with 
the additional seg pushed on the stack).

b.
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