Date: Wed, 8 Sep 2021 12:10:56 -0600 From: Warner Losh <imp@bsdimp.com> To: Colin Percival <cperciva@freebsd.org> Cc: John Baldwin <jhb@freebsd.org>, src-committers <src-committers@freebsd.org>, "<dev-commits-src-all@freebsd.org>" <dev-commits-src-all@freebsd.org>, dev-commits-src-main@freebsd.org Subject: Re: git: a8b89dff6ac0 - main - Disable acpi_timer_test by default Message-ID: <CANCZdfpMmShmTz51bG-fH-LnhnXnkQzcEOwHJCjWWwb6ZfNF7g@mail.gmail.com> In-Reply-To: <4b7bf983-8333-f4bc-6ce8-a59ac2fc7380@freebsd.org> References: <202109080132.1881WXPv069848@gitrepo.freebsd.org> <f1030cac-a17b-727a-472e-d3d90933da2b@FreeBSD.org> <4b7bf983-8333-f4bc-6ce8-a59ac2fc7380@freebsd.org>
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On Wed, Sep 8, 2021, 11:47 AM Colin Percival <cperciva@freebsd.org> wrote: > On 9/8/21 9:01 AM, John Baldwin wrote: > > On 9/7/21 6:32 PM, Colin Percival wrote: > >> Disable acpi_timer_test by default > >> This disables testing the ACPI timer by default, forcing the > use of > >> ACPI-fast rather than ACPI-safe. The broken-ACPI-timers workaround > >> can be re-enabled by setting the hw.acpi.timer_test_enabled=1 > tunable. > >> This speeds up the FreeBSD boot process by 140 ms on an EC2 > c5.xlarge > >> instance. > >> This change will not be MFCed. > >> Assuming no problems are reported, acpi_timer_test, the > associated > >> tunable, and the ACPI-safe timecounter should be removed in > FreeBSD 15. > >> Relnotes: The ACPI-safe timer is disabled in favour of > >> ACPI-fast; > >> if timekeeping issues are observed, please test > with > >> hw.acpi.timer_test_enabled=1 in loader.conf and > report > >> if that fixes the problem. > > > > Perhaps it should default to '1' for i386 and '0' otherwise? The > relevant > > chipsets were 32-bit only, so this would be a simple way to skip the > test for > > modern hardware, and you could probably MFC that safely. > > That option was discussed, but I decided that it was probably safer to > keep it enabled by default in 13 in case the test was detecting systems > which are broken in other ways. > > Googling for "ACPI-safe" (which shows up if the test fails) finds forum > discussions from the mid-2010s, but it's not clear whether that's due to > very old hardware, new ACPI timer issues, or other timekeeping problems > -- I figured it was best to play it safe for something which would be > going into a stable branch though. > I think John's suggestion is a good balance. It will also tell us if there is a need on amd64. Having it tagged as i386 also will highlight it better should the time come to remove it later. Warner -- > Colin Percival > Security Officer Emeritus, FreeBSD | The power to serve > Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid >
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