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SubjectRe: patch: delay_50ms() in ide-probe.c in 2.2.14
In <Pine.LNX.4.10.10002200721010.9714-100000@lap.arijort.home> arijort@valinux.com (arijort@valinux.com) wrote:

> Simple arithmetic tells me this patch

> a) produces same behavior as previous code, and

Are you sure ??? Jiffes is *VOLATILE* variable. And it's REALLY volatile.

> b) does it with fewer calculations.

Yes, this version does DIFFERENT thing thenoriginal one. But faster :-)

> So it has to be good, right?

No.

> But then how do we exit the while loop?

In you version it'll not happen.

> How does jiffies change?

In timer interrupt.

> This patch applies cleanly against 2.2.14
> Against 2.3.45, the relevant file is ide.c
> but otherwise, it's clean.

And it's wrong in 2.2.14 and 2.3.45 :-)


> --- drivers/block/ide-probe.c.orig Sun Feb 20 00:46:54 2000
> +++ drivers/block/ide-probe.c Sun Feb 20 07:28:32 2000
> @@ -154,8 +154,7 @@
> */
> static void delay_50ms (void)
> {
> - unsigned long timeout = jiffies + ((HZ + 19)/20) + 1;
> - while (0 < (signed long)(timeout - jiffies));
> + while (0 < (signed long)((HZ + 39)/20));
> }

> /*


P.S. "Simple arithmetic" can be VERY wrong in multithreaded program. Like linux
kernel.



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