Date: Sat, 21 Apr 2018 12:35:44 +0200 From: Gary Jennejohn <gljennjohn@gmail.com> To: Konstantin Belousov <kib@freebsd.org> Cc: Colin Percival <cperciva@tarsnap.com>, "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, Conrad Meyer <cem@freebsd.org> Subject: Re: RFC: Hiding per-CPU kernel output behind bootverbose Message-ID: <20180421123544.56d7e690@ernst.home> In-Reply-To: <20180421092049.GM6887@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> <01000162e58a466e-98f0305b-1723-467a-bc49-342c3fa9fc5b-000000@email.amazonses.com> <20180421092049.GM6887@kib.kiev.ua>
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On Sat, 21 Apr 2018 12:20:49 +0300 Konstantin Belousov <kib@freebsd.org> wrote: > On Sat, Apr 21, 2018 at 12:11:07AM +0000, Colin Percival wrote: > > 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. > I am fine with the behaviour, but I am not sure how would you implement > this. printf(9) buffers the output, you need to flush it somehow. > And printf(9) calls vprintf(9) which in turn calls _vprintf which will allocate a buffer on the stack (bad idea) if the option PRINTF_BUFR_SIZE is set in the kernel config file. So it seems that output may even be double buffered. -- Gary Jennejohn
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