Date: Mon, 16 Apr 2001 02:48:50 -0700 From: Alfred Perlstein <bright@wintelcom.net> To: Oscar-Ivan Lepe-Aldama <oscar@ac.upc.es> Cc: hackers@FreeBSD.ORG Subject: Re: Sysctl question (again) Message-ID: <20010416024850.I976@fw.wintelcom.net> In-Reply-To: <3ADABC98.B26D6C78@ac.upc.es>; from oscar@ac.upc.es on Mon, Apr 16, 2001 at 11:34:16AM %2B0200 References: <3ADABC98.B26D6C78@ac.upc.es>
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* Oscar-Ivan Lepe-Aldama <oscar@ac.upc.es> [010416 02:34] wrote:
> Hi!
> the technical question follows the next commentary. This is the second
> (third) time I post this question. I'm wondering why I haven't got any
> answers. Is it because this isn't the right forum? Is it because I
> haven't been clear enough? Is it because my bad english? Any clue on why
> the people in this forum can not give me any kind of answer for the
> following question will be aprreciated. Now, the technical question
> follows.
>
> Is there a maximum for the size of an object that sysctl can handle?
>
> I'm asking this because I have inserted in a 4.1.1 kernel an array
> defined as
>
>
> struct buf_entry {
> unsgined int id;
> u_int64_t tsc;
> u_int64_t pmec1;
> u_int64_t pmec2;
> } mybuffer[NUMENTRIES];
>
> SYSCTL_NODE(, CTL_NAVI, experiments, CTLFLAG_RW, 0,"Experiments");
> SYSCTL_OPAQUE(_experiments, OID_AUTO, buffer, CTLFLAG_RD, &mybuffer,
> sizeof(mybuffer), "", "");
>
>
> When NUMENTRIES equals 100000 (100 thousand) everything works well; that
> is, I can read the content of the array using
>
> sysctl -b experiments.mybuffer > somefile.raw
>
> But when NUMENTRIES equals 1000000 (1 million) and I use the above
> command to read the content of the array, the system stops working
> properly; that is, all virtual terminals freezed so I can't sent any
> command to the system, although the kernel seams to be alive as it
> responds to ICMP echo packets.
>
> I do want to have a large array within the kernel's memory space as I'm
> measuring the performance of some kernel's routines using the Pentium's
> Performance Monitoring Event Counters, and the more performance data I
> could get in one experiment the best.
>
> By the way, the system under test has 64 MB of RAM and 20 GB of free
> space on disk.
>
> Any explanation on the possibility or the impossibility of having such
> large array within the kernel memory-space and having it exported
> through sysctlt will be verry much appreciated.
>
uh:
struct buf_entry {
4 unsgined int id;
8 u_int64_t tsc;
8 u_int64_t pmec1;
8 u_int64_t pmec2;
} mybuffer[NUMENTRIES];
28 * 1,000,000 = 28Megs
That's quite a bit of space to wire down in your kernel, especially for
a 64meg box. I would get more ram.
You can also read on how to enable a kernel debugger and get us a meaningful
traceback in order to possibly fix the problem.
-Alfred
> Thanks,
>
> --
> ========================================================================
> 0 0 0 Oscar-Ivan Lepe-Aldama | UPC-Campus Nord, DAC
> 0 0 0 e-mail: oscar@ac.upc.es | Modul D6, despatx 116
> 0 0 0 phone: +34 93 401 7187 | Jordi Girona, 1-3
> U P C fax: +34 93 401 7055 | 08034 Barcelona - SPAIN
> WWW: http://www.ac.upc.es/homes/oscar/
> ========================================================================
>
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--
-Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org]
Instead of asking why a piece of software is using "1970s technology,"
start asking why software is ignoring 30 years of accumulated wisdom.
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