RE: [PATCH] prctl: return MCE process flags through pointer

From: Smith, GeoffX
Date: Wed Dec 23 2009 - 15:24:37 EST

Earlier today, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>> >Why are task_struct.timer_slack_ns and
>> >task_struct.default_timer_slack_ns unsigned long, btw? AFACIT we could
>> >make them unsigned ints.
>> Timer slack is not a Boolean or enum, and we want the greatest range
>possible. (Actually, I'd like to talk Arjan into using the same time
>structure as select(), but that's another discussion.) Internally hrtimer
>uses unsigned long. I know long and unsigned long are the same on some
>architectures, but let's not introduce an unnatural restriction -- recall
>that arg2 is unsigned long.
>Using unsigned ints will reduce the size of the task_struct.
>Is there any conceivable case for a timer_slack which exceeds four
>seconds? If so, what is it, and if so, why this:
>#define MAX_SLACK (100 * NSEC_PER_MSEC)

WRT to times longer than 4.2 sec -- So far my works suggests there is a good case, but it's moot because that is all I get with unsigned long on my platform. (Both int and long are 32-bit for me; x86)

WRT MAX_SLACK, select() always imposes a little slack (for non-real-time threads). The name MAX_SLACK is not actually the absolute maximum, it is only the maximum that the kernel will impose by default.

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