From nobody Sat Oct 09 19:55:13 2021 X-Original-To: freebsd-hackers@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 5211117E2134 for ; Sat, 9 Oct 2021 19:55:27 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4HRbQ66qYNz4WnY for ; Sat, 9 Oct 2021 19:55:26 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.16.1/8.16.1) with ESMTPS id 199JtD8H012056 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Sat, 9 Oct 2021 22:55:16 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua 199JtD8H012056 Received: (from kostik@localhost) by tom.home (8.16.1/8.16.1/Submit) id 199JtDon012055; Sat, 9 Oct 2021 22:55:13 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Sat, 9 Oct 2021 22:55:13 +0300 From: Konstantin Belousov To: Sebastian Huber Cc: freebsd-hackers@freebsd.org Subject: Re: Why was the timehands_count sysctl added? Message-ID: References: <2d1d2a6d-ec6b-7f52-8af3-09a833c52820@embedded-brains.de> List-Id: Technical discussions relating to FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-hackers List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-hackers@freebsd.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2d1d2a6d-ec6b-7f52-8af3-09a833c52820@embedded-brains.de> X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FROM, NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.5 X-Spam-Checker-Version: SpamAssassin 3.4.5 (2021-03-20) on tom.home X-Rspamd-Queue-Id: 4HRbQ66qYNz4WnY X-Spamd-Bar: ---- Authentication-Results: mx1.freebsd.org; none X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[] X-ThisMailContainsUnwantedMimeParts: N On Sat, Oct 09, 2021 at 09:41:28PM +0200, Sebastian Huber wrote: > Hello, > > I synchronize currently the port of the FreeBSD timecounters to RTEMS and > came across a change in 2019 which I do not understand. Some time ago the > timehands were reduced from 10 to two: > > https://reviews.freebsd.org/D7302 > > In 2019 this changed again to be up to 16: > > https://reviews.freebsd.org/D21563 This review did not changed it back to 16, the default value is still 2. It allows to bump the number of used timehands, but normally systems run with only 2. > > The corresponding sysctl is not documented: > > https://www.freebsd.org/cgi/man.cgi?query=timecounters&sektion=4 > > Does someone know why this sysctl to select the count of timehands was > added? Is this a performance optimization for some systems? To allow for experimentation, and to satisfy some requests where people wanted to have more that 2 timehands.