From owner-freebsd-geom@freebsd.org Sat Dec 28 08:40:34 2019 Return-Path: Delivered-To: freebsd-geom@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id EB0111E2C9B; Sat, 28 Dec 2019 08:40:34 +0000 (UTC) (envelope-from rizzo.unipi@gmail.com) Received: from mail-vs1-f66.google.com (mail-vs1-f66.google.com [209.85.217.66]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "smtp.gmail.com", Issuer "GTS CA 1O1" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 47lHFs2xXxz49Jg; Sat, 28 Dec 2019 08:40:33 +0000 (UTC) (envelope-from rizzo.unipi@gmail.com) Received: by mail-vs1-f66.google.com with SMTP id s16so16622971vsc.10; Sat, 28 Dec 2019 00:40:33 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=mCfwL+S9FB01e6gFVVFCCV61qTxxUPD/jYe8nyjqV28=; b=HlfBhFeNtq7y5VZQASZINGQc8U0+AZszNUjQniTeBm3lhF1jjoLm/2s1zO4py8qVTT tfiGaJ78SwVbp6RLDmkwdGvR2H1dSLnVc19vkTjSyq5gUWx+evPEmaYo2ASNX7luFEMf Hr04pNcYoFEUptbHwBZSAAaRQwp9nj9HapopbzMsZX47jvuU5JMxGU0mcJJGLKWw38Wo qYr4ZYz/N1kI7+f9FBOf8cA8x3WW9JvpWff513lyqaGurweD31nwUp5bLk0xfoPgUKap ywgtDOuktZv4gS0UqTZKhEJAXMoFhKL/5fIbfowviaiat/FjrU44RMRB7WVnR4cDgE/S oEcA== X-Gm-Message-State: APjAAAWe+1AJd1py5E8tieuC0r8fTA/pKi0+Yr625rbRnCPFw9TTXHdp w8rI3dc9mvdKFxyFB4o3thsusgPKaWNxDdi6H3o= X-Google-Smtp-Source: APXvYqxKUbNDRoSjOY7y5WzOQtCuNx8PzeT25E9Be/7QB2Q6fRKN5vNsKIqUjsPCO2DUbOnDEBbOAMvYrZKtYo8FiBk= X-Received: by 2002:a67:67c1:: with SMTP id b184mr29657164vsc.239.1577522431025; Sat, 28 Dec 2019 00:40:31 -0800 (PST) MIME-Version: 1.0 References: <6d466360-988f-e80d-3212-b6c479a5ec03@FreeBSD.org> <22559.1577484040@critter.freebsd.dk> In-Reply-To: <22559.1577484040@critter.freebsd.dk> From: Luigi Rizzo Message-ID: Subject: Re: [Probabile SPF]Re: gsched: modernize or remove? To: Poul-Henning Kamp Cc: Warner Losh , Alexander Motin , Luigi Rizzo , Pawel Jakub Dawidek , "freebsd-geom@FreeBSD.org" , "Conrad E. Meyer" , "Andrey V. Elsukov" , "freebsd-arch@freebsd.org" , Warner Losh X-Rspamd-Queue-Id: 47lHFs2xXxz49Jg X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=none; spf=pass (mx1.freebsd.org: domain of rizzounipi@gmail.com designates 209.85.217.66 as permitted sender) smtp.mailfrom=rizzounipi@gmail.com X-Spamd-Result: default: False [-2.01 / 15.00]; ARC_NA(0.00)[]; TO_DN_EQ_ADDR_SOME(0.00)[]; FROM_NEQ_ENVFROM(0.00)[rizzo@iet.unipi.it,rizzounipi@gmail.com]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; R_SPF_ALLOW(-0.20)[+ip4:209.85.128.0/17]; RCVD_TLS_ALL(0.00)[]; MIME_GOOD(-0.10)[multipart/alternative,text/plain]; MIME_TRACE(0.00)[0:+,1:+,2:~]; DMARC_NA(0.00)[unipi.it]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCVD_IN_DNSWL_NONE(0.00)[66.217.85.209.list.dnswl.org : 127.0.5.0]; RCPT_COUNT_SEVEN(0.00)[10]; NEURAL_HAM_MEDIUM(-1.00)[-0.999,0]; IP_SCORE(-1.01)[ipnet: 209.85.128.0/17(-3.11), asn: 15169(-1.88), country: US(-0.05)]; FORGED_SENDER(0.30)[rizzo@iet.unipi.it,rizzounipi@gmail.com]; RWL_MAILSPIKE_POSSIBLE(0.00)[66.217.85.209.rep.mailspike.net : 127.0.0.17]; R_DKIM_NA(0.00)[]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:209.85.128.0/17, country:US]; SUBJECT_ENDS_QUESTION(1.00)[]; TAGGED_FROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2] X-Mailman-Approved-At: Fri, 31 Jan 2020 14:58:22 +0000 Content-Type: text/plain; charset="UTF-8" X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: freebsd-geom@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: GEOM-specific discussions and implementations List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Date: Sat, 28 Dec 2019 08:40:35 -0000 X-Original-Date: Sat, 28 Dec 2019 00:40:19 -0800 X-List-Received-Date: Sat, 28 Dec 2019 08:40:35 -0000 On Fri, Dec 27, 2019 at 2:00 PM Poul-Henning Kamp wrote: > -------- > In message bA@mail.gmail.com> > , Warner Losh writes: > >On Fri, Dec 27, 2019 at 10:53 AM Alexander Motin wrote: > > > >> Hi, > >> > >> As I can see, gsched code was not really maintained for the last 10 > >> years since being added. > ... > >> So my question is: does it make sense to try fix/modernize it, or it > >> just be easier to remove it? Does anybody still use it, or see some > >> future for it? > > Gsched was always a weird thing IMO. > > I was happy to see that you could do stuff like that with GEOM, but > for the life of me I could never figure out why you would want to > do it with GEOM which is a very low-information environment when > it comes to scheduling decisions. > > I belive the original inspiration was "Anticipatory disk-scheduling" > which tries to mitigate some starvation issues which you can have > with a normal elevator disksort on systems with very few ioreq > sources[1]. > > With SSDs all but having erased seek-time from the surface of the > planet, and huge caches in drives, controllers and pretty much > everywhere else people have been able to squeeze one in, it is not > even obvious to me if it makes sense to have any disksort in the > first place[2], much less gssched. > phk's summary is perfectly accurate. the practical motivation at the time was to make sure that svn operations and streaming I/O would not kill each other, but since we all switched to SSDs there is no use case anymore and so I am ok with removing gsched. As to why it was in geom rather than elsewhere: that was a very convenient place to do scheduling in a generic way, rather than replicate it in scsi/hdd/other lower level drivers. cheers luigi