Date: Sat, 21 Apr 2018 00:11:07 +0000 From: Colin Percival <cperciva@tarsnap.com> To: Konstantin Belousov <kib@freebsd.org>, Conrad Meyer <cem@freebsd.org> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: RFC: Hiding per-CPU kernel output behind bootverbose Message-ID: <01000162e58a4670-66a9983e-c3ef-493a-a60f-c477645b5100-000000@email.amazonses.com> In-Reply-To: <20180419214550.GF6887@kib.kiev.ua> References: <01000162df15f856-1e5d2641-2a72-4250-8d8e-adcd47bc5db4-000000@email.amazonses.com> <20180419204405.GE6887@kib.kiev.ua> <CAG6CVpUerOo%2B55nJq61Hy83RYpbOZS6puEDuemspfNS12urZZw@mail.gmail.com> <20180419214550.GF6887@kib.kiev.ua>
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On 04/19/18 14:45, Konstantin Belousov wrote: > On Thu, Apr 19, 2018 at 02:37:56PM -0700, Conrad Meyer wrote: >> On Thu, Apr 19, 2018 at 1:44 PM, Konstantin Belousov wrote: >>> The 'CPU XX Launched' messages are very useful for initial diagnostic >>> of the SMP startup failures. You need to enable bootverbose to see the >>> hang details, but for initial hint they are required. Unfortunately, AP >>> startup hangs occur too often to pretend that this can be delegated to >>> very specific circumstances. >> >> Really? I don't know that I've ever seen an AP startup hang. How >> often do they occur? > > It was epidemic with Sandy Bridge, mostly correlated to specific BIOS > supplier and its interaction with the x2APIC enablement, see madt.c:170 > and below. > > There were several recent reports of the issue with Broadwell Xeon > machines, no additional data or resolution. > > There are sporadic reports of the problem, where I do not see > a clear commonality. Would it be sufficient for debugging purposes if I change the !bootverbose case from printing many lines of SMP: AP CPU #N Launched! to instead have a single SMP: Launching AP CPUs: 86 73 111 21 8 77 100 28 57 42 10 60 87 88 41 113 36 19 72 46 92 52 24 81 90 3 107 96 9 14 80 118 29 121 62 74 56 55 1 12 63 18 67 13 45 102 33 94 69 68 93 83 48 31 30 32 51 89 71 78 64 84 123 61 40 47 37 22 54 101 38 4 97 44 17 109 104 5 85 43 2 99 39 65 95 53 58 66 91 125 23 115 16 35 79 112 103 82 7 75 11 6 98 15 126 127 20 70 34 105 27 50 116 120 49 25 108 106 122 117 114 26 110 59 76 124 119 ? (With each AP printing its number as it reaches the appropriate point?) This yields almost the same gain as silencing the launch messages completely, while still allowing you to see each CPU announcing itself. -- 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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