Date: Tue, 16 Dec 2014 11:51:09 -0700 From: Warner Losh <imp@bsdimp.com> To: John Baldwin <jhb@freebsd.org> Cc: arch@freebsd.org Subject: Re: Change default VFS timestamp precision? Message-ID: <708ECB13-C3A1-46E9-BF29-6F544CC4FDE6@bsdimp.com> In-Reply-To: <201412161348.41219.jhb@freebsd.org>
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[-- Attachment #1 --] > On Dec 16, 2014, at 11:48 AM, John Baldwin <jhb@freebsd.org> wrote: > > We still ship with vfs.timestamp_precision=0 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=3). 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)? > > I can think of a few options: > > 1) Change vfs.timestamp_precision default to 3 for all systems. > > 2) Only change vfs.timestamp_precision default to 3 for amd64/i386 using an > #ifdef. > > 3) Something else? > > What do other folks think? (1). If there’s a specific kernel / platform that’s slow, we can make it an option for those kernels. Warner [-- Attachment #2 --] -----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-----home | help
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