Messages in this thread | | | Date | Sat, 12 Apr 2008 14:12:46 -0700 | From | Arjan van de Ven <> | Subject | Re: [PATCH 2/3] x86: Implement prctl PR_GET_TSC and PR_SET_TSC |
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On Sat, 12 Apr 2008 23:05:44 +0200 (CEST) Erik Bosman <ejbosman@cs.vu.nl> wrote:
> > > On Sat, 12 Apr 2008, H. Peter Anvin wrote: > > > Arjan van de Ven wrote: > > > > > > Hi, > > > > > > why did you make this a configuration option? In general it's not > > > a good idea to make userspace visible ABI's (PR_* clearly is one > > > of these) a CONFIG option unless there's some HUGE space saving > > > going on. I don't see that here.... > > > > > > So can you explain your rationale for making this a config option? > > > > > The ABI itself is not a config option (see patch 1/3.) > If the x86 implementation patch isn't applied, prctl() will > return -EINVAL, just like most other PR_* options, which are > only implemented on specific architectures, take > (PR_GET/PR_SET_ENDIAN) as an example.
that doesn't say why you made it an option still :) Something like this (which looks like generally useful functionality) should just be there unless there is a really high cost....
> > > > > I also saw no mention about performance impact, which need to be > > considered whenever *anything* is proposed to be inserted into a hot > > path. It may be (heck, *should be*) that the performance impact > > isn't measurable, but that needs to be positively established. > > > > This is why I made the implementation part configurable, although I > don't think the overhead will be very high since it seems to me that > the __switch_to_xtra function was designed explicitly to keep unusual > options out of the hot path.
so you normally don't have performance overhead unless you use the feature.... that's really good! It also means that there wouldn't be a need for this to be a config option, but instead it can just always be there.. saving us a ton of ifdefs as well as the burden of having an extra config option.
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