Re: [Perfctr-devel] Re: Enabling RDPMC in user space by default

From: Bernd Schmidt (bernds_cb1_at_t-online.de)
Date: 11/30/05

  • Next message: Greg KH: "Re: Linux 2.6.15-rc3" 
    Date:	Wed, 30 Nov 2005 00:28:22 +0100
To: Andi Kleen <ak@suse.de>

    Andi Kleen wrote:

    > To give an bad analogy RDTSC usage in the last years is
    > like explicit spinning wait loops for delays in the earlier
    > times. They tended to work on some subset of computers,
    > but were always bad and caused problems and people eventually learned
    > it was better to use operating system services for this.
    >
    > The kernel will probably not disable RDTSC outright,
    > but will make it clear in documentation that it's a bad
    > idea to use directly and laugh at everybody who runs
    > into problems with it.

    I happen to have an old program which uses RDTSC frequently for timing
    purposes. That seemed like a good idea at the time, but I guess it
    should be updated. The question is, what replacement is there? I don't
    want to have to use a syscall every 50 instructions or so. Feel free to
    laugh, but suggesting a workable replacement might be more helpful.

    Bernd
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  • Next message: Greg KH: "Re: Linux 2.6.15-rc3"