should jackd's bufsize still be a power of 2?

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bluebell
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should jackd's bufsize still be a power of 2?

Postby bluebell » Thu Mar 21, 2019 8:07 pm

I read that there were plugins that need a power of 2. But on my system xruncounter shows better results when I have multiples of 1 ms latency, that is with buffer sizes of 48, 96,192 ...

Code: Select all

configuring for 48000Hz, period = 48 frames (1.0 ms), buffer = 2 periods
Xrun 1 at DSP load 83.591034

configuring for 48000Hz, period = 64 frames (1.3 ms), buffer = 2 periods
Xrun 1 at DSP load 52.569481

configuring for 48000Hz, period = 96 frames (2.0 ms), buffer = 2 periods
Xrun 1 at DSP load 95.608429

configuring for 48000Hz, period = 128 frames (2.7 ms), buffer = 2 periods
Xrun 1 at DSP load 68.922791


My Qtractor projects seem to run fine with non-powers of 2. Are there any reasons to use only powers of 2?
Linux – MOTU UltraLite AVB – Qtractor – https://soundcloud.com/suedwestlicht

merlyn
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Re: should jackd's bufsize still be a power of 2?

Postby merlyn » Thu Mar 21, 2019 8:23 pm

It seems not. I've heard that USB interfaces work better with 3 periods. You may be able to get to ~98% DSP before an Xrun with 3 periods.

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bluebell
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Re: should jackd's bufsize still be a power of 2?

Postby bluebell » Thu Mar 21, 2019 8:30 pm

I have this effect even with n=3:

Code: Select all

configuring for 48000Hz, period = 96 frames (2.0 ms), buffer = 3 periods
Xrun 1 at DSP load 95.736221

configuring for 48000Hz, period = 128 frames (2.7 ms), buffer = 3 periods
Xrun 1 at DSP load 65.408142


At least xruncounter runs best when buffer_size/sample_rate gives whole milliseconds. The number of buffers seems to be unimportant.
Linux – MOTU UltraLite AVB – Qtractor – https://soundcloud.com/suedwestlicht

tramp
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Re: should jackd's bufsize still be a power of 2?

Postby tramp » Thu Mar 21, 2019 9:31 pm

You leave out the most important part, the circle num.
On the road again.

merlyn
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Re: should jackd's bufsize still be a power of 2?

Postby merlyn » Fri Mar 22, 2019 8:52 am

We could clarify this. Buffer sizes that are a multiple of (samplerate/1000) work best for USB devices that use isochronous transfer, and have an interval between packets of 1ms. Drumfix went into some detail on this in this post.

To attempt to put this into English: These USB devices send packets at a constant time interval, whether they need to or not. If they send a power of two buffer this will get out of step with the stream of packets. To keep the buffer and the device in sync use a buffer that will be filled every 1ms, or multiple of.

lsusb -v gives the necessary information to find out the interval between packets, although I must admit I can't see where it is.

@Bluebell it was a happy accident that your device also uses synchronous isochronous transfer, and has an interval of 1ms. If the interval was different the buffer size would be different.

So these non-power of two buffers only apply to specific devices. I have a PCI card and use a power of two buffer.

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bluebell
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Re: should jackd's bufsize still be a power of 2?

Postby bluebell » Fri Mar 22, 2019 12:28 pm

tramp wrote:You leave out the most important part, the circle num.



Code: Select all

Samplerate 48000
Buffersize is 96
jack running with realtime priority
Xrun 1 at DSP load 91.893112
Xrun 2 at DSP load 92.355820
Xrun 3 at DSP load 92.438957
Xrun 4 at DSP load 89.244476
Xrun 5 at DSP load 89.244476
Xrun 6 at DSP load 93.297241
Xrun 7 at DSP load 95.261810
Xrun 8 at DSP load 95.261810
Xrun 9 at DSP load 96.080902
Xrun 10 at DSP load 91.765457
Xrun 11 at DSP load 95.607727
in complete 11 Xruns in 9310 circles
first Xrun happen at DSP load 91.893112 circle 8909


Code: Select all

Samplerate 48000
Buffersize is 128
jack running with realtime priority
Xrun 1 at DSP load 65.227478
Xrun 2 at DSP load 67.056404
Xrun 3 at DSP load 68.142494
Xrun 4 at DSP load 67.623383
Xrun 5 at DSP load 68.880531
Xrun 6 at DSP load 69.067474
Xrun 7 at DSP load 69.067474
Xrun 8 at DSP load 66.998108
Xrun 9 at DSP load 66.998108
Xrun 10 at DSP load 66.901154
Xrun 11 at DSP load 66.901154
Xrun 12 at DSP load 66.702637
Xrun 13 at DSP load 67.559875
Xrun 14 at DSP load 67.559875
Xrun 15 at DSP load 66.281815
Xrun 16 at DSP load 66.281815
Xrun 17 at DSP load 66.281815
Xrun 18 at DSP load 66.299194
Xrun 19 at DSP load 66.299194
Xrun 20 at DSP load 67.133095
Xrun 21 at DSP load 67.133095
Xrun 22 at DSP load 66.762344
Xrun 23 at DSP load 67.214630
Xrun 24 at DSP load 67.872131
Xrun 25 at DSP load 71.322845
Xrun 26 at DSP load 71.322845
Xrun 27 at DSP load 69.326096
Xrun 28 at DSP load 69.326096
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Xrun 30 at DSP load 69.326096
Xrun 31 at DSP load 69.326096
Xrun 32 at DSP load 66.227188
Xrun 33 at DSP load 68.034821
Xrun 34 at DSP load 68.034821
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Xrun 36 at DSP load 68.034821
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Xrun 38 at DSP load 68.034821
Xrun 39 at DSP load 64.475021
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Xrun 42 at DSP load 66.089722
Xrun 43 at DSP load 66.089722
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Xrun 46 at DSP load 64.834061
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Xrun 50 at DSP load 65.837891
Xrun 51 at DSP load 65.837891
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Xrun 54 at DSP load 65.837891
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Xrun 56 at DSP load 63.657883
Xrun 57 at DSP load 63.657883
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Xrun 59 at DSP load 63.657883
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Xrun 100 at DSP load 63.911945
Xrun 101 at DSP load 63.911945
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Xrun 172 at DSP load 54.822266
Xrun 173 at DSP load 54.822266
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Xrun 175 at DSP load 54.822266
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Xrun 177 at DSP load 55.243092
Xrun 178 at DSP load 55.243092
Xrun 179 at DSP load 55.243092
Xrun 180 at DSP load 55.243092
Xrun 181 at DSP load 55.243092
Xrun 182 at DSP load 55.243092
Xrun 183 at DSP load 55.243092
Xrun 184 at DSP load 55.243092
Xrun 185 at DSP load 55.243092
Xrun 186 at DSP load 55.243092
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Xrun 188 at DSP load 54.797089
Xrun 189 at DSP load 54.797089
Xrun 190 at DSP load 54.797089
Xrun 191 at DSP load 54.797089
Xrun 192 at DSP load 54.797089
Xrun 193 at DSP load 54.797089
Xrun 194 at DSP load 54.797089
Xrun 195 at DSP load 54.797089
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Xrun 197 at DSP load 54.517822
Xrun 198 at DSP load 54.517822
Xrun 199 at DSP load 54.517822
Xrun 200 at DSP load 54.517822
Xrun 201 at DSP load 54.517822
Xrun 202 at DSP load 54.517822
Xrun 203 at DSP load 54.517822
Xrun 204 at DSP load 54.517822
Xrun 205 at DSP load 54.517822
Xrun 206 at DSP load 54.517822
Xrun 207 at DSP load 56.872566
Xrun 208 at DSP load 56.872566
Xrun 209 at DSP load 56.872566
Xrun 210 at DSP load 56.872566
Xrun 211 at DSP load 56.872566
Xrun 212 at DSP load 56.872566
Xrun 213 at DSP load 56.872566
Xrun 214 at DSP load 56.872566
Xrun 215 at DSP load 56.872566
Xrun 216 at DSP load 56.872566
Xrun 217 at DSP load 56.872566
Xrun 218 at DSP load 55.649338
Xrun 219 at DSP load 55.649338
Xrun 220 at DSP load 55.649338
Xrun 221 at DSP load 55.649338
Xrun 222 at DSP load 55.649338
Xrun 223 at DSP load 55.649338
Xrun 224 at DSP load 55.649338
Xrun 225 at DSP load 55.649338
Xrun 226 at DSP load 55.649338
Xrun 227 at DSP load 55.649338
Xrun 228 at DSP load 54.906441
Xrun 229 at DSP load 54.906441
Xrun 230 at DSP load 54.906441
Xrun 231 at DSP load 54.906441
Xrun 232 at DSP load 54.906441
Xrun 233 at DSP load 54.906441
Xrun 234 at DSP load 54.906441
Xrun 235 at DSP load 54.906441
Xrun 236 at DSP load 54.906441
Xrun 237 at DSP load 54.906441
Xrun 238 at DSP load 54.906441
Xrun 239 at DSP load 75.540237
Xrun 240 at DSP load 75.540237
Xrun 241 at DSP load 75.540237
Xrun 242 at DSP load 75.540237
Xrun 243 at DSP load 75.540237
Xrun 244 at DSP load 75.540237
Xrun 245 at DSP load 75.540237
Xrun 246 at DSP load 75.540237
Xrun 247 at DSP load 75.540237
Xrun 248 at DSP load 75.540237
Xrun 249 at DSP load 66.521057
Xrun 250 at DSP load 66.521057
Xrun 251 at DSP load 66.521057
Xrun 252 at DSP load 66.521057
Xrun 253 at DSP load 66.521057
Xrun 254 at DSP load 66.521057
Xrun 255 at DSP load 66.521057
Xrun 256 at DSP load 66.521057
Xrun 257 at DSP load 66.521057
Xrun 258 at DSP load 80.822418
Xrun 259 at DSP load 80.822418
Xrun 260 at DSP load 80.822418
Xrun 261 at DSP load 80.822418
Xrun 262 at DSP load 80.822418
Xrun 263 at DSP load 80.822418
Xrun 264 at DSP load 80.822418
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Xrun 266 at DSP load 80.822418
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Xrun 268 at DSP load 80.822418
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Xrun 270 at DSP load 69.255920
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Xrun 272 at DSP load 69.255920
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Xrun 275 at DSP load 69.255920
Xrun 276 at DSP load 69.255920
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Xrun 278 at DSP load 69.255920
Xrun 279 at DSP load 69.255920
Xrun 280 at DSP load 84.271622
Xrun 281 at DSP load 84.271622
Xrun 282 at DSP load 84.271622
Xrun 283 at DSP load 84.271622
Xrun 284 at DSP load 84.271622
Xrun 285 at DSP load 84.271622
Xrun 286 at DSP load 84.271622
Xrun 287 at DSP load 84.271622
Xrun 288 at DSP load 84.271622
Xrun 289 at DSP load 84.271622
Xrun 290 at DSP load 70.024033
Xrun 291 at DSP load 70.024033
Xrun 292 at DSP load 70.024033
Xrun 293 at DSP load 70.024033
Xrun 294 at DSP load 70.024033
Xrun 295 at DSP load 70.024033
Xrun 296 at DSP load 70.024033
Xrun 297 at DSP load 70.024033
Xrun 298 at DSP load 70.024033
Xrun 299 at DSP load 70.024033
Xrun 300 at DSP load 70.024033
Xrun 301 at DSP load 64.006760
Xrun 302 at DSP load 64.006760
Xrun 303 at DSP load 64.006760
Xrun 304 at DSP load 64.006760
Xrun 305 at DSP load 64.006760
Xrun 306 at DSP load 64.006760
Xrun 307 at DSP load 64.006760
Xrun 308 at DSP load 64.006760
Xrun 309 at DSP load 64.006760
Xrun 310 at DSP load 64.006760
Xrun 311 at DSP load 64.006760
Xrun 312 at DSP load 80.109161
Xrun 313 at DSP load 80.109161
Xrun 314 at DSP load 80.109161
Xrun 315 at DSP load 80.109161
Xrun 316 at DSP load 80.109161
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Xrun 319 at DSP load 80.109161
Xrun 320 at DSP load 80.109161
Xrun 321 at DSP load 80.109161
Xrun 322 at DSP load 67.961563
Xrun 323 at DSP load 67.961563
Xrun 324 at DSP load 67.961563
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Xrun 329 at DSP load 67.961563
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Xrun 331 at DSP load 67.961563
Xrun 332 at DSP load 67.961563
Xrun 333 at DSP load 83.980782
Xrun 334 at DSP load 83.980782
Xrun 335 at DSP load 83.980782
Xrun 336 at DSP load 83.980782
Xrun 337 at DSP load 83.980782
Xrun 338 at DSP load 83.980782
Xrun 339 at DSP load 83.980782
Xrun 340 at DSP load 83.980782
Xrun 341 at DSP load 83.980782
Xrun 342 at DSP load 83.980782
Xrun 343 at DSP load 83.980782
Xrun 344 at DSP load 70.666313
Xrun 345 at DSP load 70.666313
Xrun 346 at DSP load 70.666313
Xrun 347 at DSP load 70.666313
Xrun 348 at DSP load 70.666313
Xrun 349 at DSP load 70.666313
Xrun 350 at DSP load 70.666313
Xrun 351 at DSP load 70.666313
Xrun 352 at DSP load 70.666313
Xrun 353 at DSP load 70.666313
Xrun 354 at DSP load 82.970062
Xrun 355 at DSP load 82.970062
Xrun 356 at DSP load 82.970062
Xrun 357 at DSP load 82.970062
Xrun 358 at DSP load 82.970062
Xrun 359 at DSP load 82.970062
Xrun 360 at DSP load 82.970062
Xrun 361 at DSP load 82.970062
Xrun 362 at DSP load 82.970062
Xrun 363 at DSP load 82.970062
Xrun 364 at DSP load 82.970062
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Xrun 366 at DSP load 89.234467
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Xrun 370 at DSP load 89.234467
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Xrun 429 at DSP load 97.574783
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Xrun 437 at DSP load 97.574783
in complete 437 Xruns in 11190 circles
first Xrun happen at DSP load 65.227478 circle 8584
Linux – MOTU UltraLite AVB – Qtractor – https://soundcloud.com/suedwestlicht

merlyn
Established Member
Posts: 477
Joined: Thu Oct 11, 2018 4:13 pm

Re: should jackd's bufsize still be a power of 2?

Postby merlyn » Fri Mar 22, 2019 10:43 pm

Bluebell wrote:

Code: Select all

first Xrun happen at DSP load 91.893112 circle 8909

That looks healthy.

To test a theory I'll predict the speed of your processor. I'll use your 128 result because I have a 128 result for my 2.6 GHz system.

Code: Select all

first Xrun happen at DSP load 99.948204 circle 8809


You got 65% at cycle 8584. First scale that up to 100%. 8584 * 100/65 = 13206.

Now apply that to processor speed. 2.6 * 13206 / 8809 = 3.90.

As far as I know 3.9 Ghz processors don't exist, so I'd say your processor is 3.8 GHz.

User avatar
bluebell
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Posts: 1129
Joined: Sat Sep 15, 2012 11:44 am
Location: Saarland & Frankfurt, Germany

Re: should jackd's bufsize still be a power of 2?

Postby bluebell » Sat Mar 23, 2019 11:59 am

merlyn wrote:
Bluebell wrote:

Code: Select all

first Xrun happen at DSP load 91.893112 circle 8909

That looks healthy.

To test a theory I'll predict the speed of your processor. I'll use your 128 result because I have a 128 result for my 2.6 GHz system.

Code: Select all

first Xrun happen at DSP load 99.948204 circle 8809


You got 65% at cycle 8584. First scale that up to 100%. 8584 * 100/65 = 13206.

Now apply that to processor speed. 2.6 * 13206 / 8809 = 3.90.

As far as I know 3.9 Ghz processors don't exist, so I'd say your processor is 3.8 GHz.


cat /proc/cpuinfo: Intel(R) Core(TM) i7-7700T CPU @ 2.90GHz

cpufreq-info: current CPU frequency is 3.67 GHz

Good estimate.
Linux – MOTU UltraLite AVB – Qtractor – https://soundcloud.com/suedwestlicht


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