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From: paul@vixie.UUCP
Newsgroups: comp.unix.wizards
Subject: Why "u." and not "u->" ?  (I'm reading Bach book)
Message-ID: <626@vixie.UUCP>
Date: Tue, 12-May-87 01:48:08 EDT
Article-I.D.: vixie.626
Posted: Tue May 12 01:48:08 1987
Date-Received: Thu, 14-May-87 04:47:35 EDT
Reply-To: paul@vixie.UUCP (Paul Vixie Esq)
Distribution: world
Organization: Vixie Enterprises, San Francisco
Lines: 16

According to Bach, UNIX(tm) rearranges the kernel's virtual address space
to make the 'u' structure variable map to the current process' u-area.  This
requires that the U area be page-aligned and a multiple of pagesize long,
which sounds a little bit difficult to do.  But that's not my question...

Mapping the u-area onto 'u.' certainly makes references quicker than using a
structure pointer, since there is one less memory reference before getting to
members of the structure.  What I wonder is, how much jumbling is required to
re-map the page, and is the trade-off worth it?  Just how much is 'u.' used
between context switches, anyway?

-- 
Paul A. Vixie        {ptsfa, crash, winfree}!vixie!paul
329 Noe Street       dual!ptsfa!vixie!paul@ucbvax.Berkeley.EDU
San Francisco        
CA  94116            paul@vixie.UUCP     (415) 864-7013