Subject: Re: some performance diff with getc()/putc() between FreeBSD and
To: Paul Ripke <firstname.lastname@example.org>
From: Stephan Uphoff <email@example.com>
Date: 05/06/2003 14:23:59
Paul Ripke wrote:
> OK, what concerns me is those "random seeks/sec" rates. There's a huge
> difference there, and that could hurt other stats. It shouldn't be CPU
> bound (obviously), the only thing that comes to mind is in disk
> I/O scheduling - disksort. I wonder what the difference is.
> [alternately, maybe I'm spending too much time looking at DBMS at work]
I would suspect the read ahead to be the culprit, since it reads in an
extra 128 KByte, when a random read (rounded up by file the file system
block size) ends at a 64KByte boundary. (see genfs_getpages())
Block-sized random reads on a filesystem with 8K blocks would read
an average of three blocks for every block requested.