Date: Wed, 08 Jun 2022 08:25:49 +0000 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Sebastian Huber <sebastian.huber@embedded-brains.de> Cc: Konstantin Belousov <kostikbel@gmail.com>, hackers@freebsd.org Subject: Re: pps_capture() and pps_fetch() Message-ID: <202206080825.2588PnVl065319@critter.freebsd.dk> In-Reply-To: <8ced022c-518a-4a77-135f-37d58cde27e7@embedded-brains.de> References: <5b8310db-c94b-709f-8c57-bec2d413a80f@embedded-brains.de> <202206010725.2517PEfF036703@critter.freebsd.dk> <e1093df0-c719-0421-3e96-c6d7df861a51@embedded-brains.de> <YphDlMyWxDWvJo5Q@kib.kiev.ua> <c4fe6a08-24b6-522e-3963-cf03eb994496@embedded-brains.de> <202206030828.2538ScDg080165@critter.freebsd.dk> <35d4d55c-ff62-cff7-cdbf-ea2549dee86c@embedded-brains.de> <202206031847.253Il6Y2082105@critter.freebsd.dk> <8ced022c-518a-4a77-135f-37d58cde27e7@embedded-brains.de>
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-------- Sebastian Huber writes: > tc_min_ticktock_freq =3D max(1, tc->tc_frequency / > (((uint64_t)tc->tc_counter_mask + 1) / 3)); > > code in tc_windup(). I don't understand the value "3" here, I guess it > should depend on timehands_count? Not really. The divide by three is holding a good distance to the half-way mark, so that we "wind" to the next hand before the roll-over introduces s ambiguity. The number of timehands relate to how bad latency (interrupt and scheduling) can be for kernel threads. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
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