Messages in this thread | | | Date | Thu, 1 Nov 2001 10:34:53 -0500 (EST) | From | "Richard B. Johnson" <> | Subject | Re: [Patch] Re: Nasty suprise with uptime |
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On Thu, 1 Nov 2001, vda wrote:
> On Thursday 01 November 2001 00:52, Tim Schmielau wrote: > > > OK, absolutely last patch for today. Sorry to bother everyone, but the > > jiffies wraparound logic was broken in the previous patch. > > > > As stated before, I would kindly ask for widespread testing PROVIDED IT IS > > OK FOR YOU TO RISK THE STABILITY OF YOUR BOX! > > I see you dropped jiffies_hi update in timer int. > IMHO argument on wasting 6 CPU cycles or so per each timer int: > > - jiffies++; > + if(++jiffies==0) jiffies_hi++; > > is not justified. I'd rather see simple and correct code in timer int > rather than jumping thru the hoops in get_jiffies_64(). > > For CPU cycle saving zealots: I advocate saving 2 static longs in get_jiffies > instead :-) > -- > vda > -
Well not exactly zealots. I test a lot of stuff. In fact, the code you propose:
if(++jiffies==0) jiffies_hi++;
... actually works quite well:
Script started on Thu Nov 1 10:23:54 2001 # ./chk Simple bump = 13 Bump chk and incr = 15 # ./chk Simple bump = 13 Bump chk and incr = 15 # ./chk Simple bump = 13 Bump chk and incr = 15 # exit exit Script done on Thu Nov 1 10:24:08 2001
It adds only two CPU clock cycles if (iff) the 'C' compiler is well behaved.
Test code is appended. In the test code, I calculate everything, then print the results. This is so the 'C' library + system call doesn't mess up the cache. Note this if you use this as a template to test other questionable code snippets.
Cheers, Dick Johnson
Penguin : Linux version 2.4.1 on an i686 machine (799.53 BogoMips).
I was going to compile a list of innovations that could be attributed to Microsoft. Once I realized that Ctrl-Alt-Del was handled in the BIOS, I found that there aren't any.
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