Date: Mon, 21 Jan 2002 00:03:27 -0800 From: Terry Lambert <tlambert2@mindspring.com> To: raman@hello.to Cc: stable@freebsd.org, current@freebsd.org Subject: Re: Extended paging bug in Athlon affect FreeBSD? Message-ID: <3C4BCB4F.60F1D4FC@mindspring.com> References: <20020121030018.7425.qmail@web14006.mail.yahoo.com>
next in thread | previous in thread | raw e-mail | index | archive | help
Raman Ng wrote: > I don't know what mailing list this mail should be > posted to, sorry if it is posted to the wrong mailing > list. > > Recently I found Linux 2.4 kernel is affected by the > bug of extended paging in AMD Athlon through the > following link. I don't know if FreeBSD is also > affected. > > http://linuxtoday.com/news_story.php3?ltsn=2002-01-21-001-20-NW-KN I am well aware of this bug. It does not affect FreeBSD, which only uses 4M pages for the first 4M of the kernel itself. I've worked on code that enables 4M pages on other memory used in FreeBSD, that had this problem, but only if you were really stupid in your allocation mechanism. There's a workaround for this problem which is fairly trivial to implement in software, and should probably be done when 4M pages are enabled, if you are using an Athlon, and are adding 4M pages. The problem didn't bite my own application, since I knew about it and used the TLBs in a very specific way to get around the problem, but I'm told that after I left the company, someone went in and used them a different way, not knowing about the problem or the workaround, and broke things. This resulted in about a 14% performance loss. If you are doing heavy networking on a machine with a lot of memory, it's reasonable to move your mbufs into 4M pages, which nets you a 4-14% improvement (depending on whether or not you also change your allocator: 14% if you do). If you do that, knowing how to work around the problem nets you a pretty big win in overall performance, for about 6-10 more machine instructions at startup time. 8-). In any case, this will not be a problem for FreeBSD, and is only a problem for Linux because of the strange way they initialize things. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?3C4BCB4F.60F1D4FC>