From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: base64 Subject: dvb usb issues since kernel 4.9 From: Mike Galbraith Message-Id: <1515553368.8252.5.camel@gmx.de> Date: Wed, 10 Jan 2018 04:02:48 +0100 To: Jesper Dangaard Brouer , Mauro Carvalho Chehab Cc: Linus Torvalds , Peter Zijlstra , Alan Stern , Ingo Molnar , Josef Griebichler , Greg Kroah-Hartman , USB list , Eric Dumazet , Rik van Riel , Paolo Abeni , Hannes Frederic Sowa , linux-kernel , netdev , Jonathan Corbet , LMML , David Miller List-ID: T24gVHVlLCAyMDE4LTAxLTA5IGF0IDIyOjI2ICswMTAwLCBKZXNwZXIgRGFuZ2FhcmQgQnJvdWVy IHdyb3RlOgo+IAo+IEkndmUgcHJldmlvdXNseSBleHBlcmllbmNlZCB0aGF0IHlvdSBjYW4gYmUg YWZmZWN0ZWQgYnkgdGhlIHNjaGVkdWxlcgo+IGdyYW51bGFyaXR5LCB3aGljaCBpcyBhZGp1c3Rh YmxlICh3aXRoIENPTkZJR19TQ0hFRF9ERUJVRz15KToKPiAKPiAgJCBncmVwIC1IIC4gL3Byb2Mv c3lzL2tlcm5lbC9zY2hlZF8qX2dyYW51bGFyaXR5X25zCj4gIC9wcm9jL3N5cy9rZXJuZWwvc2No ZWRfbWluX2dyYW51bGFyaXR5X25zOjIyNTAwMDAKPiAgL3Byb2Mvc3lzL2tlcm5lbC9zY2hlZF93 YWtldXBfZ3JhbnVsYXJpdHlfbnM6MzAwMDAwMAo+IAo+IFRoZSBhYm92ZSBudW1iZXJzIHdlcmUg Y29uZmlybWVkIG9uIHRoZSBSUGkyIChzZWVbMl0pLiBXaXRoIGNvbW1pdAo+IDRjZDEzYzIxYjIw NyAoInNvZnRpcnE6IExldCBrc29mdGlycWQgZG8gaXRzIGpvYiIpLCBJIGV4cGVjdC9hc3N1bWUg dGhhdAo+IHNvZnRpcnEgcHJvY2Vzc2luZyBsYXRlbmN5IGlzIGJvdW5kZWQgYnkgdGhlIHNjaGVk X3dha2V1cF9ncmFudWxhcml0eV9ucywKPiB3aGljaCB3aXRoIDMgbXMgaXMgbm90IGdvb2QgZW5v dWdoIGZvciB0aGVpciB1c2UtY2FzZS4KCk5vdGUgb2YgY2F1dGlvbiB3cnQgdHdpZGRsaW5nwqBz Y2hlZF93YWtldXBfZ3JhbnVsYXJpdHlfbnM6IGl0IG11c3QKcmVtYWluIDwgc2NoZWRfbGF0ZW5j eV9ucy8yIGVsc2UgeW91IGVmZmVjdGl2ZWx5IGRpc2FibGUgd2FrZXVwCnByZWVtcHRpb24gY29t cGxldGVseSwgdHVybmluZyBDRlMgaW50byBhIHRpY2sgZ3JhbnVsYXJpdHkgc2NoZWR1bGVyLgoK CS1NaWtlCi0tLQpUbyB1bnN1YnNjcmliZSBmcm9tIHRoaXMgbGlzdDogc2VuZCB0aGUgbGluZSAi dW5zdWJzY3JpYmUgbGludXgtdXNiIiBpbgp0aGUgYm9keSBvZiBhIG1lc3NhZ2UgdG8gbWFqb3Jk b21vQHZnZXIua2VybmVsLm9yZwpNb3JlIG1ham9yZG9tbyBpbmZvIGF0ICBodHRwOi8vdmdlci5r ZXJuZWwub3JnL21ham9yZG9tby1pbmZvLmh0bWwK From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mout.gmx.net ([212.227.17.22]:58950 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751564AbeAJDDc (ORCPT ); Tue, 9 Jan 2018 22:03:32 -0500 Message-ID: <1515553368.8252.5.camel@gmx.de> Subject: Re: dvb usb issues since kernel 4.9 From: Mike Galbraith To: Jesper Dangaard Brouer , Mauro Carvalho Chehab Cc: Linus Torvalds , Peter Zijlstra , Alan Stern , Ingo Molnar , Josef Griebichler , Greg Kroah-Hartman , USB list , Eric Dumazet , Rik van Riel , Paolo Abeni , Hannes Frederic Sowa , linux-kernel , netdev , Jonathan Corbet , LMML , David Miller Date: Wed, 10 Jan 2018 04:02:48 +0100 In-Reply-To: <20180109222604.64d4377c@redhat.com> References: <20180109154235.2a42f0a0@vento.lan> <20180109222604.64d4377c@redhat.com> Content-Type: text/plain; charset="ISO-8859-15" Mime-Version: 1.0 Content-Transfer-Encoding: 8BIT Sender: linux-media-owner@vger.kernel.org List-ID: On Tue, 2018-01-09 at 22:26 +0100, Jesper Dangaard Brouer wrote: > > I've previously experienced that you can be affected by the scheduler > granularity, which is adjustable (with CONFIG_SCHED_DEBUG=y): > > $ grep -H . /proc/sys/kernel/sched_*_granularity_ns > /proc/sys/kernel/sched_min_granularity_ns:2250000 > /proc/sys/kernel/sched_wakeup_granularity_ns:3000000 > > The above numbers were confirmed on the RPi2 (see[2]). With commit > 4cd13c21b207 ("softirq: Let ksoftirqd do its job"), I expect/assume that > softirq processing latency is bounded by the sched_wakeup_granularity_ns, > which with 3 ms is not good enough for their use-case. Note of caution wrt twiddling sched_wakeup_granularity_ns: it must remain < sched_latency_ns/2 else you effectively disable wakeup preemption completely, turning CFS into a tick granularity scheduler. -Mike