Re: a joint letter on low latency and Linux

[Neil Brown]

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.

NeilBrown