Date: Tue, 3 Apr 2012 19:31:24 +0200 From: Gary Jennejohn <gljennjohn@googlemail.com> To: Jerry Toung <jrytoung@gmail.com> Cc: freebsd-hackers <freebsd-hackers@freebsd.org> Subject: Re: CAM disk I/O starvation Message-ID: <20120403193124.46ad9de9@ernst.jennejohn.org> In-Reply-To: <CADC0LV=-e%2B7PshRQdc69e2-Vktf6XFpVrqiMpx=QL4m_%2B9hSnw@mail.gmail.com> References: <CADC0LV=-e%2B7PshRQdc69e2-Vktf6XFpVrqiMpx=QL4m_%2B9hSnw@mail.gmail.com>
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On Mon, 2 Apr 2012 10:55:31 -0700 Jerry Toung <jrytoung@gmail.com> wrote: > I am convinced that there is a bug in the CAM code that leads to I/O starvation. > I have already discussed this privately with some. I am now bringing this up to > the general audience to get more feedback. > I've observed this with my onboard ATI IXP700 AHCI SATA controller and 2 or 3 SATA disks. When one disk gets busy all others are pretty much blocked until it finishes. Seems to me that this behavior is (fairly) recent. [snip] > I have a patch and it fixes those problems. I can share it to the list > if requested to. > da0 and da1 now both automatically get 126 openings and based on that, > extra logic implements fairness in cam/cam_xpt.c. No more 0 MB/s on > da1. This is on 8.1-RELEASE FreeBSD. > It would be interesting to see your patch. I always run HEAD but maybe I could use it as a base for my own mods/tests. -- Gary Jennejohn
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