Re: finding out the value of HZ from userspace

From: Peter Williams (peterw_at_aurema.com)
Date: 03/16/04

  • Next message: Jeff Garzik: "Re: Prism54 Driver Project Complete" 
    Date:	Tue, 16 Mar 2004 16:53:25 +1100
To: Andi Kleen <ak@muc.de>

    Andi Kleen wrote:
    > Peter Williams <peterw@aurema.com> writes:
    >
    >
    >>This horrible hack of converting all tick values to 100 (from 1000)
    >>for export to user space because a large number of user space programs
    >>assume that HZ is 100 would NOT be necessary if there was a mechanism
    >>whereby user space programs could find out how many ticks there are in
    >>a second instead of having to make assumptions.
    >
    >
    > Already exists for a long time - AT_CLKTCK. glibc has a nice wrapper
    > for it too (sysconf)

    So it does and POSIX.1 (_SC_CLK_TCK) compliant as well. Unfortunately,
    the presence of this functionality makes it VERY difficult to understand
    why ticks are being converted from HZ==1000 values to HZ=100 values when
    they are being exported to user space especially as this conversion
    throws away precision. Can anyone enlighten me?

    Peter 

    -- 
Dr Peter Williams, Chief Scientist                peterw@aurema.com
Aurema Pty Limited                                Tel:+61 2 9698 2322
PO Box 305, Strawberry Hills NSW 2012, Australia  Fax:+61 2 9699 9174
79 Myrtle Street, Chippendale NSW 2008, Australia http://www.aurema.com
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