<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="margin: 0px;" class="">Hi all,</div><div style="margin: 0px; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px;" class="">This is my first post here. I’m note new to audio programming or linux, but I haven’t done much in terms of combining the two. Most of my audio programming has been on os x.</div><div style="margin: 0px; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px;" class="">Currently working on some realtime convolution with lots of channels and low latency requirements, but I am running into some unexpected cpu-spikes and hope some of you might have an idea of possible causes.</div><div style="margin: 0px; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px;" class="">I’m processing 32 sample-blocks at 48KHz but roughly every 0,6 seconds I get a large spike in cpu usage. This cannot possibly be explained by my algorithm, because the load should be pretty stable. </div><div style="margin: 0px; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px;" class="">I am measuring cpu load by getting the time with <span style="font-size: 11px; font-family: Menlo;" class="">clock_gettime(CLOCK_MONOTONIC_RAW, timespec*) </span>at the beginning and end of each callback. When converted to a percentage my cpu load hovers somewhere between 40 an 50% most of the time, but more or less every 900 callbacks (0.8 seconds there is a spike of more than 100%.</div><div style="margin: 0px; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px;" class="">I am not doing any IO, mallocing or anything else that could block. My threads are SCHED_FIFO with max priority (I have 4 threads on 4 cores).</div><div style="margin: 0px;" class="">The only explanation I can come up with is that my threads are somehow pre-empted even though there are realtime threads. Is that even possible? And is there a way to check this? Besides pre-emption maybe my caches are severely thrashed but i find that unlikely as it seems to happen on all 4 cores simultaneously. </div><div style="margin: 0px; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px;" class="">I’m running (more or less default install, no additional services run-in) Linux Mint 17.3 with a 3.19.0-42-lowlatency kernel on a core i7-6700 with hyperthreading/turbo disabled.</div><div style="margin: 0px; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px;" class="">I remember reading somewhere that realtime threads cannot run more than .95s every second. That would be very bad if it actually meant my threads are blocked run for a period of 50ms straight…</div><div style="margin: 0px; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px; min-height: 14px;" class="">Anyone have any thoughts on possible causes?</div><div style="margin: 0px; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px;" class="">best,</div><div style="margin: 0px;" class="">Fokke</div><div style="margin: 0px; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px; min-height: 14px;" class=""><br class=""></div></body></html>