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From: Terry Lambert <terry@lambert.org>
Message-Id: <199705121841.LAA07971@phaeton.artisoft.com>
Subject: Re: mmap()
To: vadim@tversu.ac.ru (Vadim Kolontsov)
Date: Mon, 12 May 1997 11:41:45 -0700 (MST)
Cc: freebsd-hackers@FreeBSD.ORG
In-Reply-To: <19970512115004.56026@tversu.ac.ru> from "Vadim Kolontsov" at May 12, 97 11:50:05 am
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>   this question must be old, but anyway...
> 
>   why mmap() under freebsd (at least, 2.1) almost two times slower than
> read()? I've tryed to read large files, with multiple mmap()'ing file into 
> buffer with size = getpagesize() * 10, and with/without madvise()...

Because of the way buffering is implemented, mmap() can not trigger
predictive read-ahead, while read() can.  The performance improvement
in read() for sequential I/O comes from read-ahead.


					Regards,
					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.