Another question that's been bugging me -- this is behavior that seems
identical in 2216/2217 and not related to my ealier performance degredation
post.
I run VMware. It runs w/144Mg and writes out a 153M suspend file when I
suspend it to disk. My system has a total of 512M, so the entire
suspend file gets written to the disk buffers pronto (often under 1 second).
But a 'sync' done afterwards can take anywhere from 20-40 seconds.
vmstat shows a maximum b/o rate of 700, with 200-500 being typical.
So, I know that the maximum write rate through the disk cache is
close to 10,000 blocks/second. So why when the disk cache of a
large file is 'sync'ed out, do I get such low b/o rates?
Two sample 'vmstat 5' outputs during a sync were:
1 0 0 6292 13500 254572 165712 0 0 1 0 119 282 1 1
98
2 0 0 6292 13444 254572 165716 0 0 0 702 279 534 0 2
98
1 1 0 6292 13444 254572 165716 0 0 0 501 352 669 0 1
99
0 1 0 6292 13444 254572 165716 0 0 0 520 372 697 0 2
97
1 0 0 6292 13444 254572 165716 0 0 0 510 367 694 0 2
98
0 1 0 6292 13444 254572 165716 0 0 0 694 379 715 0 2
98
1 0 1 6292 13444 254572 165716 0 0 0 618 391 964 0 2
98
0 1 1 6292 13444 254572 165716 0 0 0 441 302 765 0 1
98
0 0 0 6292 13496 254572 165716 0 0 0 63 180 355 1 1
99
0 0 0 6292 13496 254572 165716 0 0 0 0 103 195 0 1
99
----and
0 0 0 6228 18836 246036 167824 0 0 0 0 232 563 6 13
82
0 1 0 6228 18784 246036 167824 0 0 0 506 175 489 2 1
97
1 0 0 6228 18780 246036 167824 0 0 0 292 305 647 0 1
99
0 1 0 6228 18780 246036 167824 0 0 0 253 285 602 0 1
99
0 1 0 6228 18780 246036 167824 0 0 0 226 289 612 0 1
99
1 0 0 6228 18832 246036 167824 0 0 0 157 199 406 0 1
99
0 0 0 6228 18832 246036 167824 0 0 0 0 101 240 1 1
99
---
Another oddity -- If you add up the rates in the 2nd example, and multiply
the average rate by 5, you get around 5200 blocks written out (for a 152M
file).
Note that a du on it shows it to use 155352, so it isn't that it is sparse.
Is vmstat an unreliable measure? The above tests were on a 2216 system.
-l
--
L A Walsh | Trust Technology, Core Linux, SGI
[email protected] | Voice/Vmail: (650) 933-5338
I'm working on some timer routines to allow arbitrary numbers of timers
all based off the single real timer provided by "setitimer". However, I
haven't been able to figure out from the documentation what happens to
the countdown timer used by setitimer when the system clock is changed
(by root, for instance). If I move the system clock forward or backward
a few seconds, is the itimer affected by this at all (I hope not) or can
I simply ignore it (I hope so).
Thanks,
Chris
--
Chris Friesen | MailStop: 043/33/F10
Nortel Networks | work: (613) 765-0557
3500 Carling Avenue | fax: (613) 765-2986
Nepean, ON K2H 8E9 Canada | email: [email protected]