Date: Tue, 17 Apr 2012 12:30:15 -0700 From: Adrian Chadd <adrian@freebsd.org> To: gljennjohn@googlemail.com Cc: freebsd-hackers <freebsd-hackers@freebsd.org>, Jerry Toung <jrytoung@gmail.com> Subject: Re: CAM disk I/O starvation Message-ID: <CAJ-VmomN3j=aJW%2BUfg73SUu6JzV0=PtMUVARnxeup7XEJ8Fbmg@mail.gmail.com> In-Reply-To: <20120417211558.4793b705@ernst.jennejohn.org> References: <CADC0LV=-e%2B7PshRQdc69e2-Vktf6XFpVrqiMpx=QL4m_%2B9hSnw@mail.gmail.com> <20120403193124.46ad9de9@ernst.jennejohn.org> <CADC0LVm1HY2Dz%2BVk_GK35szRS6ySviLhMiL1TSRBOnPwQnBwRg@mail.gmail.com> <20120411192153.5672b62c@ernst.jennejohn.org> <CAJ-VmokwR%2BVHmup6OLN%2BBGHvoAeLvJ9%2BBeZ9Fm6xM7Pio73pzQ@mail.gmail.com> <20120417211558.4793b705@ernst.jennejohn.org>
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On 17 April 2012 12:15, Gary Jennejohn <gljennjohn@googlemail.com> wrote:
> Yes, I agree completely. =A0My first thought was that disk I/O
> scheduling had somehow been pessimized. =A0But then I thought -
> wait a minute, I have disk caches enabled and command queuing is
> enabled for all of them, so that shouldn't really have any
> noticeable impact. =A0So I was at a loss to explain why disk performance
> had suddenly gotten so bad.
That's assuming there are no bugs anywhere. :)
> I'd be willing to spend some time on diagnosing it, but I have to come
> up with a scenario which would reliably reproduce the problem. =A0AFAICR
> it generally happened when I was running csup/svn because my CVS
> repositoy is on one disk and /usr/{ports,src} are on a different one.
>
> I still have the old problem kernel around, but it's probably not
> instrumented for any meaningful diagnoses.
Well do you know which version of which tree you used to build that?
If it's head, you could "just" keep an earlier source tree around to
build a kernel from.
Adrian
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