Date: Tue, 2 Dec 2008 09:41:22 +1100 From: "Jan Mikkelsen" <janm@transactionware.com> To: <jhrett@netconsonance.com>, "'FreeBSD Stable'" <freebsd-stable@freebsd.org> Subject: Re: no priority on the console? Message-ID: <1A7634CAC3E147CB8B5CDA853E4856D7@STUDYPC>
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Hi, > As per my previous message, I've spent about 3 months trying to debug = > a problem that was causing all disk I/O to go very slowly. A first glance this sounds similar to the problem I am having with very = slow I/O on the Areca controller. (see: "7.1-PRERELEASE: arcmsr write performance problem") What controller are you using? Is the write = cache enabled? > One of the things which made this nearly impossible to diagnose was =20 > the absolute lack of priority given to the console. Logging in on the = =20 > console would take 12-15 minutes. Hitting enter on the console would = > usually take between 3 and 5 minutes. Yes, I see this when I get the slow I/O problem. I think this has been = a problem for some time; I have also seen "console freezes" (ssh, console, etc.) on 6.0 and 6.1 systems under SATA load. That was a while ago now (2006?). I also recall others reporting have seen the same problem intermittently. > This doesn't seem right to me. Can someone explain why the console =20 > isn't given a very high priority? Why not? What other mechanism does = =20 > the sysadmin have for debugging, at a time when SSH logins either =20 > fail, or take up to an hour to complete? In my case I could log into the system and start things like iostat and gstat and they kept running while the problem occurred so that I could = see some of what was going on. I could also have what seemed like a = reasonable ssh session with a jail on the same machine. This indicates to me that = it is not the console that is the issue, but rather that the process of = logging into the main machine touches some file that causes it to get caught up = in the slow I/O quagmire. If the problem I am seeing now is the same as the one I saw a few years = ago then I think the nature might have changed. My recollection is that utilities like iostat would also freeze back then, but I can't be sure. I'd like to resolve this problem too. Regards, Jan.
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