Date: Thu, 15 Jan 2004 10:11:53 -0800 (PST) From: Nate Lawson <nate@root.org> To: Dag-Erling =?iso-8859-1?q?Sm=F8rgrav?= <des@des.no> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/kern init_main.c kern_descrip.c sys_pipe.c uipc_syscalls.c uipc_usrreq.c vfs_syscalls.c src/sys/sys filedesc.h Message-ID: <20040115101021.L71463@root.org> In-Reply-To: <xzpwu7tignh.fsf@dwp.des.no> References: <200401151015.i0FAF49u009868@repoman.freebsd.org> <xzpwu7tignh.fsf@dwp.des.no>
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On Thu, 15 Jan 2004, Dag-Erling [iso-8859-1] Sm=F8rgrav wrote: > Tim Robbins <tjr@freebsd.org> writes: > > Thanks for committing this. I'm interested, though, what was the reason= you > > changed it to use a single bitmap instead of two levels? > > The increased complexity didn't actually translate into a performance > improvement. There was no reason to use two levels instead of one. > The theoretical advantage is logarithmic rather than linear early > growth, but in practice it wasn't noticeable. The cost of the logic > required to maintain and use the high-level bitmap outweighs the gain > (which is to save a handful of comparisons against zero in the > low-level bitmap). A related question, why wasn't sys/bitstring.h used? -Nate
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