> On Fri, Sep 03, 1999 at 12:51:04PM -0500, Mark H. Wood wrote:
> > There's still a problem though, if I understand sysctl's argument
> > structure: you can only fetch (or set) one thing at a time. That means
> > that a monitoring tool could be causing quite a lot of context-switching.
>
> a syscall isn't a context-switch. I remember hearing someone say that
> mingo has patches to bring it down to 30us. That's not a lot :-)
OK, I picked the wrong word. A thing that takes time out to save/restore
registers, does evil things to the TLB and the cache, etc. It's worth
minimizing these if the cost of doing so isn't too high.
> > A better way would be (say) a sysctln() that would take a whole list of
> > items and return them all in a single pair of context switches.
> > (*Setting* N items in one call leads to difficulties with partial success,
> > so maybe it should be a read-only sysjustshowmen(). :-)
>
> Like readv/writev?
If you're saying that the arguments would look like a list of iovecs, yes
to some extent. There'd have to be another field in the descriptor to
specify *what* was wanted, since there'd be no ordering imposed on the
items you could ask for. [Crowd murmurs: he's a VMS-head, he's talking
about SYS$GETSYI()! Stone him!]
If you're saying that one should just use readv on a handle to some /proc
file, no -- people play with the layout of /proc files all the time so
there's no good way to know what counts to put in the sortof-iovecs.
(Now you know my "other reasons" for doing it this way. You can't be
blindsided by encoding and formatting changes if there's no encoding or
formatting.)
-- Mark H. Wood, Lead System Programmer mwood@IUPUI.Edu A Brazil-nut is neatly packaged and tightly integrated. To turn it into food, you must crack and remove the shell. I find that I feel the same way about an increasing number of software products. *sigh*
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