Messages in this thread |  | | From | "LA Walsh" <> | Subject | writing out disk cache | Date | Mon, 13 Nov 2000 13:52:39 -0800 |
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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 law@sgi.com | Voice/Vmail: (650) 933-5338
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