From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Time resolution in Emacs Date: Mon, 25 Apr 2022 08:34:04 -0700 Organization: UCLA Computer Science Department Message-ID: <3008dea1-572b-9010-f3c4-15272145fd8a@cs.ucla.edu> References: <5ed963b2-3fa8-48d8-627e-bc0571d15b43@gmail.com> <2dd15844-01b3-0144-740c-185ec8488a81@cs.ucla.edu> <4a23f3a4-fe8f-d396-49d8-10034803be63@gmail.com> <52fb10fb-892a-f273-3be8-28793f27e204@cs.ucla.edu> <5cd820d4-ae67-43d4-9e63-c284d51ff1e4@gmail.com> <83tuapvcxs.fsf@gnu.org> <6efc5d24-34a2-fd30-cd20-fe4ac3e48310@cs.ucla.edu> <83fsm8tdzl.fsf@gnu.org> <9e4781b2-2ffa-b1ce-09b4-ead82cad9038@cs.ucla.edu> <83ilr3siku.fsf@gnu.org> <4e41671c-fae8-61c4-845c-4c7ba4317e88@cs.ucla.edu> <83fsm7sh2s.fsf@gnu.org> <83czhbsgc2.fsf@gnu.org> <33fb24fb-282b-cc13-a597-e7b63f19982d@cs.ucla.edu> <83y1zzq6kd.fsf@gnu.org> <837d7hr8s3.fsf@gnu.org> <83h76kq5c6.fsf@gnu.org> <9afbcc3d-b57c-b5bf-e4f6-52b352f99af8@cs.ucla.edu> <83bkwspa1r.fsf@gnu.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="29568"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Cc: manikulin@gmail.com, emacs-devel@gnu.org To: Eli Zaretskii Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Mon Apr 25 17:34:47 2022 Return-path: Envelope-to: ged-emacs-devel@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1nj0jf-0007ZV-Jp for ged-emacs-devel@m.gmane-mx.org; Mon, 25 Apr 2022 17:34:47 +0200 Original-Received: from localhost ([::1]:46234 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nj0je-0006IU-C7 for ged-emacs-devel@m.gmane-mx.org; Mon, 25 Apr 2022 11:34:46 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:55374) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nj0j2-0005be-DB for emacs-devel@gnu.org; Mon, 25 Apr 2022 11:34:08 -0400 Original-Received: from zimbra.cs.ucla.edu ([131.179.128.68]:55574) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nj0j0-000854-L3; Mon, 25 Apr 2022 11:34:07 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 5F3481600D1; Mon, 25 Apr 2022 08:34:05 -0700 (PDT) Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id kNRyWr8KTp_Z; Mon, 25 Apr 2022 08:34:04 -0700 (PDT) Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 9565E1600D4; Mon, 25 Apr 2022 08:34:04 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id ULE5VFbxMiiF; Mon, 25 Apr 2022 08:34:04 -0700 (PDT) Original-Received: from [192.168.1.9] (cpe-172-91-119-151.socal.res.rr.com [172.91.119.151]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id 6A2731600D1; Mon, 25 Apr 2022 08:34:04 -0700 (PDT) Content-Language: en-US In-Reply-To: <83bkwspa1r.fsf@gnu.org> Received-SPF: pass client-ip=131.179.128.68; envelope-from=eggert@cs.ucla.edu; helo=zimbra.cs.ucla.edu X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.io gmane.emacs.devel:288859 Archived-At: On 4/22/22 23:51, Eli Zaretskii wrote: >> There are Gnulib library functions to >> deal with this sort of thing; it's not a new problem. > > Doesn't that slow down applications? Not significantly, no. file-attributes already has the file's filesystem ID and timestamps so Emacs can easily cache that (it's a small cache with only one entry per filesystem). There's no need to traipse through the filesystem looking at other files. This is what coreutils does and it works well in practice. It's not expensive and not that complicated. Your suggestion of maintaining a static table for known filesystem types is a good one; we could do that to improve common cases. I would like to take a look into doing this. If successful, it should improve coreutils and other GNU apps even if Emacs makes no changes in this area. In the meantime I'll withdraw the proposed changes that would cause Emacs to communicate OS timestamp resolution to the user; that sort of thing can wait until after I've had that look (assuming I ever find the time :-). > what about other sources of time data? For example, timestamps > from other systems (like in your NTP example), timestamps that are > reported by Tramp functions, etc.? How do we reliably estimate the > accuracy of those? For example, if Emacs imports from the network a timestamp with three digits after the decimal point, it should convert it to an internal timestamp with millisecond resolution. Conversely when sending a textual timestamp, Emacs should generate only as many trailing digits as needed. This sort of thing is not perfect (nothing to do with timestamps is :-), but it is better than losing whatever resolution information is available.