Date: Mon, 30 Dec 2019 21:36:29 +0000 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Warner Losh <imp@bsdimp.com> Cc: Alexander Motin <mav@freebsd.org>, Alexey Dokuchaev <danfe@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all <svn-src-all@freebsd.org>, svn-src-head <svn-src-head@freebsd.org> Subject: Re: svn commit: r356185 - in head: lib/geom lib/geom/sched sys/geom sys/geom/sched sys/modules/geom sys/modules/geom/geom_sched sys/sys Message-ID: <27204.1577741789@critter.freebsd.dk> In-Reply-To: <CANCZdfoWiD9zsBJE8U%2BPM5LyLSKLgQu9m2pvdkUFbuccv_q-Qg@mail.gmail.com> References: <201912292116.xBTLG4kV012809@repo.freebsd.org> <20191230113243.GA58338@FreeBSD.org> <CANCZdfq-BGXpeUHpC1MLH2kfjHvkmB8VKuGsQX6=P9EsGs=LPA@mail.gmail.com> <20191230170208.GA20424@FreeBSD.org> <5a97d344-8741-3b8e-b6dd-b8e4cfa05aeb@FreeBSD.org> <CANCZdfoWiD9zsBJE8U%2BPM5LyLSKLgQu9m2pvdkUFbuccv_q-Qg@mail.gmail.com>
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-------- In message <CANCZdfoWiD9zsBJE8U+PM5LyLSKLgQu9m2pvdkUFbuccv_q-Qg@mail.gmail= .com>, Warner Losh writes: >I never enabled it because I never had a good car size as the default. I'= m >guessing it's somewhere on the order of 2 times the queue size in >hardware, but with modern drives I think phk might be right and that >disabling disksort entirely might be optimal, or close to optimal. I think that is a given for SSDs. For disks I fear it would be a model-by-model determination. The situation is quite different for "traditional" and shingled drives for instance, or if, God forbid, the rumours are true and we'll see IBM3380-style dual head assemblies in the market again. I guess the kernel could turn the disksort on/off a few times and only leave it on if it improves things. But first, Somebody Should=E2=84=A2 benchmark to see if disksort *ever* is= an improvement on contemporary disks. Poul-Henning PS: If somebody really want to improve disk- and ssd- performance, the low-hanging fruit is to write a log-structured storage engine under UFS, to make life easier for flash-adaptation layers and shingling drives. -- = Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe = Never attribute to malice what can adequately be explained by incompetence= .
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