Messages in this thread | | | From | Benno Senoner <> | Subject | Latency: Mingo's lowlatency patch still not perfect, but looking good | Date | Mon, 2 Aug 1999 00:45:35 +0200 |
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Hi, I performed new latency tests using the Mingo's lowlatency-2.2.10-N2 patch
The /proc stress test is now perfect, latencies max 2.5ms. The "latency jitter" in all stress tests is much lower than on a unpatched kernel. The figures are looking really flat.
Unfortunately the patch gives me still problem on disk I/O, as usual I performed the tests with mem=256m , mem=128m and mem=64m
With mem=256m I get up to 28ms on the disk write test, with mem=128m the latency goes down to 20ms and with mem=64m I get about 11ms.
The read test with mem=256m sometime gives me 5-6ms latencies and with mem=64m the latency goes down to about 3.5ms. Seems that we still need to tweak thing to get below 5ms reliably on the disk read test.
The problems seem to be still correlated to the RAM size, Ideas about which kernel function could cause this ?
here the tests: (note the decrease of latencies with reducing ramsize)
mem=256m http://www.gardena.net/benno/linux/audio/2.2.10-mingo2-256m-1/3x256.html
mem=128m http://www.gardena.net/benno/linux/audio/2.2.10-mingo2-128m-1/3x256.html
mem=64m http://www.gardena.net/benno/linux/audio/2.2.10-mingo2-64m-1/3x256.html
Note that the write performance of writing a large file decreases by about 30% using Mingo's patch, and looking at the harddisk led, the led flashes intermittently instead of being always on. The disk read perfomance is ok, it's the same like on an unpatched kernel.
Another fact to note is that re-running the same test a second time, gives me better values, than the first test after a reboot , is this maybe related to memory page allocation / buffering ?
It would be interesting to hear about the values that other people gets using mingo's patches on PII (UP) +EIDE + large RAM ?
comments ?
regards, Benno.
-- Benno Senoner E-Mail: sbenno@gardena.net Linux scheduling latency benchmarks http://www.gardena.net/benno/linux/audio
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