Re: [RFC][PATCH] iowait statistics

[William Lee Irwin III]

On Wed, 15 May 2002, Denis Vlasenko wrote:
>> I think two patches for same kernel piece at the same time is
>> too many. Go ahead and code this if you want.

On Wed, May 15, 2002 at 01:13:33PM -0300, Rik van Riel wrote:
> OK, here it is.   Changes against yesterday's patch:
> 1) make sure idle time can never go backwards by incrementing
>    the idle time in the timer interrupt too (surely we can
>    take this overhead if we're idle anyway ;))
> 2) get_request_wait also raises nr_iowait_tasks (thanks akpm)
> This patch is against the latest 2.5 kernel from bk and
> pretty much untested. If you have the time, please test
> it and let me know if it works.

Boots compiles and runs on an 4-way physical HT box. I didn't wake
the evil twins to cut down on the number of variables so it stayed
4-way despite the ability to go 8-way.

Sliding window of 120 seconds, sampled every 15 seconds, under a
repetitive kernel compile load:

Wed May 15 09:56:37 PDT 2002
cpu  60701 0 5137 203545 9327
cpu0 15048 0 1566 50868 2298
cpu1 15257 0 1176 50818 2392
cpu2 15248 0 1346 50802 2247
cpu3 15148 0 1049 51057 2390

Wed May 15 09:56:52 PDT 2002
cpu  66304 0 5543 203545 9327
cpu0 16460 0 1656 50868 2298
cpu1 16606 0 1330 50818 2392
cpu2 16655 0 1441 50802 2247
cpu3 16583 0 1116 51057 2390

Wed May 15 09:57:07 PDT 2002
cpu  71877 0 5980 203545 9327
cpu0 17849 0 1769 50868 2298
cpu1 17972 0 1466 50818 2392
cpu2 18060 0 1539 50802 2247
cpu3 17996 0 1206 51057 2390

Wed May 15 09:57:22 PDT 2002
cpu  77446 0 6420 203545 9327
cpu0 19269 0 1852 50868 2298
cpu1 19328 0 1612 50818 2392
cpu2 19448 0 1653 50802 2247
cpu3 19401 0 1303 51057 2390

Wed May 15 09:57:37 PDT 2002
cpu  83031 0 6843 203545 9327
cpu0 20699 0 1924 50868 2298
cpu1 20704 0 1738 50818 2392
cpu2 20846 0 1757 50802 2247
cpu3 20782 0 1424 51057 2390

Wed May 15 09:57:52 PDT 2002
cpu  87432 0 7216 204779 9328
cpu0 21788 0 2000 51205 2298
cpu1 21737 0 1845 51180 2393
cpu2 21871 0 1806 51230 2247
cpu3 22036 0 1565 51164 2390

Wed May 15 09:58:07 PDT 2002
cpu  93003 0 7653 204779 9328
cpu0 23178 0 2112 51205 2298
cpu1 23134 0 1950 51180 2393
cpu2 23281 0 1898 51230 2247
cpu3 23410 0 1693 51164 2390

Wed May 15 09:58:22 PDT 2002
cpu  98583 0 8082 204779 9328
cpu0 24538 0 2254 51205 2298
cpu1 24521 0 2065 51180 2393
cpu2 24704 0 1978 51230 2247
cpu3 24820 0 1785 51164 2390

It looks very constant, not sure if it should be otherwise.

Cheers,
Bill