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SubjectRe: Interesting scheduling times
Date
In article <6trfc3$io7$1@palladium.transmeta.com>,
Linus Torvalds <torvalds@transmeta.com> wrote:
>In article <199809170431.OAA20382@vindaloo.atnf.CSIRO.AU>,
>Richard Gooch <rgooch@atnf.csiro.au> wrote:
>>
>>More importantly, I'm surprised by the slowdown from 2.1.104 to
>>2.1.122-pre2.
>
>What happened is that the very latest 2.1.x kernels are using a software
>context switch, rather than just a jump through a task-gate and using
>the hardware context switch code.

Happily I checked some more, just to make sure, and profiled the kernel.

Yes, it happened during the switch-over to a software task-switch
routine, but the reason the numbers got worse for some people is simply
that I screwed up the floating point save code, and it saved _every_
time through instead of doing the lazy save it was meant to do.

The effect of this is not huge, but it's certainly noticeable. With
that fixed, the software context switch is pretty comparable to the
hardware one.

2.1.123 should have this context switch slowdown fixed.

Linus

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