From owner-freebsd-arch@FreeBSD.ORG Tue Dec 16 18:56:34 2014 Return-Path: Delivered-To: arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 539F7526 for ; Tue, 16 Dec 2014 18:56:34 +0000 (UTC) Received: from mail-pd0-f169.google.com (mail-pd0-f169.google.com [209.85.192.169]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 23ACCBFD for ; Tue, 16 Dec 2014 18:56:34 +0000 (UTC) Received: by mail-pd0-f169.google.com with SMTP id z10so14541281pdj.0 for ; Tue, 16 Dec 2014 10:56:27 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:sender:subject:mime-version:content-type:from :in-reply-to:date:cc:message-id:references:to; bh=2JdBuv3lOkB4duIuqqvLs3SEZaUucwoFHvvxOjDarP4=; b=DiHUjGcGVD66ELO7r5xRvT5l8mLiV3Sq140+Zm8VsDYeaLRID0SdbFhZ9IB0H2BQWX QdHl+dEzLAGz1ZX1KDtlxQMeEtX+0gM3g590SyiNzQzZWxMJcO10Co66DaWiobIfo4yc 23AV7ab3bCRi8goK7//wLbLytWRAEKuRQShTfMYIBWvoZB4qjr6FQBIHeQg6zSGVgpJ9 CFO8zFu/uvhPkacLV9yPr8E9GGHxJch9GY+vkKjLgKTTjN5QdbOjvyQzzAw+USQlVamv BB508QXKsh+ckNxPh9M9km3xw1W9IRFSWZBLkELT5O3EuJ/88sGGMc5ShcNo8n9Ob0pn BTFw== X-Gm-Message-State: ALoCoQlJOuyEn/k0GjbKmREgwpB4SJ7V2gcs1Fh1nYEaDVC072Nj42WgmvP+SuEw7fcKYCP4b4LH X-Received: by 10.68.134.3 with SMTP id pg3mr41933843pbb.84.1418755873251; Tue, 16 Dec 2014 10:51:13 -0800 (PST) Received: from [10.64.27.55] ([69.53.236.236]) by mx.google.com with ESMTPSA id uq15sm1721146pab.8.2014.12.16.10.51.11 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 16 Dec 2014 10:51:12 -0800 (PST) Sender: Warner Losh Subject: Re: Change default VFS timestamp precision? Mime-Version: 1.0 (Mac OS X Mail 8.1 \(1993\)) Content-Type: multipart/signed; boundary="Apple-Mail=_75C1AB44-77FF-4500-9498-506EA83706C7"; protocol="application/pgp-signature"; micalg=pgp-sha512 X-Pgp-Agent: GPGMail 2.5b3 From: Warner Losh In-Reply-To: <201412161348.41219.jhb@freebsd.org> Date: Tue, 16 Dec 2014 11:51:09 -0700 Message-Id: <708ECB13-C3A1-46E9-BF29-6F544CC4FDE6@bsdimp.com> References: <201412161348.41219.jhb@freebsd.org> To: John Baldwin X-Mailer: Apple Mail (2.1993) Cc: arch@freebsd.org X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 16 Dec 2014 18:56:34 -0000 --Apple-Mail=_75C1AB44-77FF-4500-9498-506EA83706C7 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > On Dec 16, 2014, at 11:48 AM, John Baldwin wrote: >=20 > We still ship with vfs.timestamp_precision=3D0 by default meaning that = VFS > timestamps have a granularity of one second. It is not unusual on = modern > systems for multiple updates to a file or directory to occur within a = single > second (and thus share the same effective timestamp). This can break = things > that depend on timestamps to know when something has changed or is = stale (such > as make(1) or NFS clients). On hardware that has a cheap timecounter, = I we > should use the most-precise timestamps (vfs.timestamp_precision=3D3). = However, > I'm less sure of what to do for other cases such as i386/amd64 when = not using > TSC, or on other platforms. OTOH, perhaps you aren't doing lots of = heavy I/O > access on a system with a slow timecounter (or if you are doing heavy = I/O, > slow timecounter access won't be your bottleneck)? >=20 > I can think of a few options: >=20 > 1) Change vfs.timestamp_precision default to 3 for all systems. >=20 > 2) Only change vfs.timestamp_precision default to 3 for amd64/i386 = using an > #ifdef. >=20 > 3) Something else? >=20 > What do other folks think? (1). If there=E2=80=99s a specific kernel / platform that=E2=80=99s = slow, we can make it an option for those kernels. Warner --Apple-Mail=_75C1AB44-77FF-4500-9498-506EA83706C7 Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJUkH8eAAoJEGwc0Sh9sBEAAVYP/2Nx/+9TZzzn2gSxQJUgMGCh pxG+gTtbxjJsVOOXHF2TYtZg49d8AadDTFzyqngbmEfapKuxCjF2Vqd5YpUrRl96 KnZADWOOSV0ZdojOPVQ3fJYzHu0pK3SH4x36hDLyO7Zrlh75fCzFH/eO6c3IbGmW ViAOQ7PP1S4BvOPYmGv2yG5UiWyLUbyOjlw/QB4SxgbTnzOwCxqqx8l+bFz1Jccq 3f0+pTuJS3RWCelQ0YZQVBZwgBCh+i3FBosZOUFjYNrtu6vETZa8kfs5i7vkEvMJ gJV2PO8sVaCBrwR3nm57YSDlC6NobwFcK7R9l5f8/h0clBNH1xlsM+/vu19SjHma J8gKoWMWf1ASezuQL8sWHh3hg35ymsGFhmNYLFu3HOnNWM5zKEd6d+b4GR+t324L 0i8QA/p1vfe4DJeBn1mJXmRxdgJAn+VrEJi3iJHg7HJ3TJL93th8d5G3BjFebik7 MO83umZnl+hvL8LrLp/SfK2b5RNo91v8zHedGFMcvc5pdz1jpKVmA+IZOO4Lv1cf rzDX7+q2cfQHptPB5BGjpFQ1F499/WBYvx5fkyzbk02MlEPqGoisFeRN/VN+/ECv +eT/kzISez56c5HuweShzna4JpVeCbEH5XtKIiO8AQU7kJrIWX5cPMsJB4Dk+GWa q3fvu5LRvKzxN1KNDEv/ =AS9o -----END PGP SIGNATURE----- --Apple-Mail=_75C1AB44-77FF-4500-9498-506EA83706C7--