Re: a joint letter on low latency and Linux

[Richard Gooch]

Neil Brown writes:
> On Friday June 30, [e-mail] wrote:
> > 
> > We've had this debate before. Linus said that there are two versions
> > of HZ: one for the kernel and one for user-space. The user-space one
> > should not change. All time values reported to user-space should be
> > absolute units, or jiffie values should be convert to the user-space
> > HZ units.
> > 
> > Then the kernel can run the timer tick at whatever rate it likes.
> 
> Sounds like a sensible idea, but what is the conversion factor?
> Is there a "UHZ", and I multiply a jiffie count by UHZ/HZ before
> reporting it to user space?  I noticed a "AHZ" in acct.h.  Is that
> what should be used.
> 
> I am keen to know because knfsd uses jiffies to report thread usage
> stats (the "th" line in /proc/net/rpc/nfsd) and I would like to
> present those numbers in a way that is not dependant on the value of
> HZ.  Ofcourse I could choose to report them in milliseconds, but if
> there is a standard "user-space HZ", it would be best to use that.

I think Linus favoured reporting stuff in real units.

				Regards,

					Richard....
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