Messages in this thread | | | Subject | Re: Linux 2.4.19-pre5 | From | Ed Sweetman <> | Date | 30 Mar 2002 18:48:35 -0500 |
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Due to evolution's really cool way of wrapping my emails. . i'll attach the results.
In this test I wanted to see this lag. So i switched between virtual desktops (i have 5) and used irc (eterm + epic). What i saw was lower priority (meaning processes with bigger nice values) at one specific spot in the test would stop responding but all processes at the same priority level would continue merrily. I'd say about 5/6 of the way through the test is where the lower priority processes would stop responding for a couple seconds. But they revived pretty quickly, only paused my typing for a couple moments. I failed to see any lag at all during the entire test on like-wise prioritized processes. I wouldn't have even known i was running the test if my cpu temp wasn't climbing so high and the load wasn't 256 on procmeter3.
As for the throughput debate that always follows the preempt kernel. I think it really depends on the kind of io you're doing. It really depends on what the program is trying to do with it's io. Programs that want to throttle and like to do that sequentially, probably wont appretiate you stopping it and reading some other part of the disk for a bit and have it have to go back to where it stopped. Almost no userland non-monolithic database apps actually do something like that. None that i've come into contact with. But you choose what works for your workload. if i'm running a app that wants control over the io to itself, i run it with a higher priority than other processes and you've basically taken away the "preemptiveness" factor and you get normal kernel performance (theoretically). seems logical.
Anyway I digress. I mean to get into the latency aspect. Sequential writes is scary but that's to be expected on ext3. Random reads is a concern though. It shouldn't be that high. although it was high in all the tests i ran compared to the other three. Run #2: /usr/bin/tiotest -t 256 -f 8 -r 15 -b 4096 -d . -T
File size in megabytes, Blk Size in bytes. Read, write, and seek rates in MB/sec. Latency in milliseconds. Percent of requests that took longer than 2 and 10 seconds.
Sequential Reads File Blk Num Avg Maximum Lat% Lat% CPU Kernel Size Size Thr Rate (CPU%) Latency Latency >2s >10s Eff ---------------------------- ------ ----- --- ------------------------------------------------------------ 2.4.19-pre4-ac3-preempt 2048 4096 256 9.46 5.271% 181.668 30992.77 3.60280 0.05836 179
Random Reads File Blk Num Avg Maximum Lat% Lat% CPU Kernel Size Size Thr Rate (CPU%) Latency Latency >2s >10s Eff ---------------------------- ------ ----- --- ------------------------------------------------------------ 2.4.19-pre4-ac3-preempt 2048 4096 256 0.67 0.980% 2446.793 14462.86 39.66145 0.00000 68
Sequential Writes File Blk Num Avg Maximum Lat% Lat% CPU Kernel Size Size Thr Rate (CPU%) Latency Latency >2s >10s Eff ---------------------------- ------ ----- --- ------------------------------------------------------------ 2.4.19-pre4-ac3-preempt 2048 4096 256 5.36 5.029% 160.584 209853.98 0.42915 0.37536 107
Random Writes File Blk Num Avg Maximum Lat% Lat% CPU Kernel Size Size Thr Rate (CPU%) Latency Latency >2s >10s Eff ---------------------------- ------ ----- --- ------------------------------------------------------------ 2.4.19-pre4-ac3-preempt 2048 4096 256 0.67 0.533% 0.047 4.50 0.00000 0.00000 125
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