In article
<7366de24-bc1c-47f1-9fc1-6de7d66d6e5a@[EMAIL PROTECTED]
>,
Stargazer <spamtrap@[EMAIL PROTECTED]
> wrote:
>Hi,
>
>I am writing my own real-time kernel for x86. Now I face something
>really strange (or may be rather it's not; it has been some time since
>I was in the details of x86 microarchitecture).
>
>I measured CPU clocks elapsed between the first assembly instruction
>executed at interrupt's entry point in IDT and beginning of the C code
>of user-defined interrupt handler and the result was a big
>surprise :-) It took about 2500 cycles despite that I have only a
>handful of assembly instructions before a call to user-supplied IRQ
>handler.
>
>A little more testing showed that almost all cycles (2300+) were spent
>at access to a global variable (via ds:[] addressing).
Is this a SINGLE memory access or several/many accesses?
>Nothing that
>accesses stack memory (push, pop, call, mov) makes a noticeable
>difference. Does anybody have an idea why this happens? I test on
>Celeron 2.8G in protected mode set up for flat model with paging
>disabled.
>
>I can post the code of the interrupt's entry point (until the C entry
>point is called), but it's rather trivial and not long.
Please feel free to post the code so there doesn't have to be any
unnecessary speculation.
Patrick
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