Re: [Perfctr-devel] Re: Enabling RDPMC in user space by default
From: Bernd Schmidt
Date: Tue Nov 29 2005 - 18:29:57 EST
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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