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SubjectRe: lowlatency-2.2.13-A1 questions

On Tue, 30 Nov 1999, William Montgomery wrote:

> The udelay_resched(n) macro does not seem to reference "n",

(yep, thats a bug)

> would the following be an acceptable implementation?
> #define udelay_resched(n) (\
> { int i; \
> for (i = 0; i < ((n+9)/10); i++) { \
> conditional_schedule(); \
> udelay(10); \
> } \
> })

yep, thats ok.

> I have been using the lowlatency-2.2.10-N6B.patch with good results.
> I recently installed the 2.2.13 kernel and applied the lowlatency-2.2.13-A1
> patch, however the results were not quite as good. The 2.2.10-N6B patch
> on the 2.2.10 kernel gave +/-500usec scheduling latencies whereas
> the 2.2.13-A1 patch on the kernel gave +/-3msec latencies. Any idea
> why? These results were obtained on a Pentium III 500MHz.

the 2.2.13 patches do not have the console changes - and text console
scrollback is introducing latencies around 4msec. The reason is that
occasionally the console driver has to read+copy the whole (text)
videoram, and this is slow. I solved this by adding a read-cache for all
videoram contents, thus videoram only ever has to be written. (which is

> How were the high latency areas identified? I would be very happy
> to help in testing and contributing to this patch.

i'll eventually forward port the console changes as well.

-- mingo

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