Date: Wed, 04 Jun 2014 21:56:44 +0300 From: Alexander Motin <mav@FreeBSD.org> To: Jung-uk Kim <jkim@FreeBSD.org>, Chris Torek <torek@torek.net> Cc: freebsd-hackers@freebsd.org Subject: Re: kern.timecounter.smp_tsc_adjust Message-ID: <538F6BEC.6070300@FreeBSD.org> In-Reply-To: <538F5C53.7060208@FreeBSD.org> References: <201406041732.s54HWDlE032048@elf.torek.net> <538F5C53.7060208@FreeBSD.org>
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On 04.06.2014 20:50, Jung-uk Kim wrote: > On 2014-06-04 13:32:13 -0400, Chris Torek wrote: >>> In any case, at least one, and maybe two, routines need their >>> types changed (and maybe the TSC_READ macro as well). Is it OK >>> to just assume the upper 32 bits are in sync? >> >> For whatever it may be worth, the following patch (to change >> everything to 64 bits) is boot-tested and no longer crashes the >> system that did crash with the unpatched version. It also >> successfully synchronized TSCs at least once (Intel based board >> with the "invariant TSC" bit set, 40 CPUs). >> >> Chris >> >> x86/tsc: fix SMP TSC adjustment code >> >> On SMP systems, if kern.timecounter.smp_tsc is set, the kernel >> attempts to determine whether the TSCs on the processors are >> sufficiently in-sync to be used for time counting. If not, and >> kern.timecounter.smp_tsc_adjust is set, we then attempt to adjust >> all the TSCs. >> >> The adjustment code assumed we kept a full 64-bit value for each >> TSC, but the data-gathering and comparison code used 32-bit values. >> As a result, if the timecounters were out of sync, the adjustment >> code could crash (depending on the number of CPUs). >> >> This converts everything to full 64-bit values. > ... > > It was done on head almost two years ago: > > http://svnweb.freebsd.org/changeset/base/239133 > > I guess mav forgot to MFC r239133 before r250772 (CC'ed): > > http://svnweb.freebsd.org/changeset/base/250772 Merged to stable/9. Thanks for the reminder. -- Alexander Motin
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