From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6CAB2315D33 for ; Tue, 25 Nov 2025 11:50:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764071416; cv=none; b=fqwGwqzNmgixRdpGf1kUzhytLUZMUrWqk3mlk5iwKkIBx/cIstW0j3FXrWL8laXC3CYJZZcqsOeGjLI1bm1uK4dqmU2Y+q8McsKarC5dM+72Ocir9uH5Cz4c++dxFnxePn0b+9yPVcz8QCFgZWusD88xypaBib50FMDqB5Y1TfI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764071416; c=relaxed/simple; bh=RdgaI9xnQgTkOLjm4s4aEPNh5q7spfN35W2Oaen9+UM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=FRPw/XgaozQHub3U0VN7MIhFm7ZMdqzfOq0fRyPBDjGpDD7kmzz1OP+F2MnXcijqmAEcCOI2MsFCGeUvEuL5xAFoG5s4LuC2hLh5BRfpTUf56wDA7jXtG+FC6ebJRbcMg2m5dw4cBzgOtFDOSwOgsWcWzCwkJ5nJMi3mgs6N9sw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=ntuiy2le; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=5R42N7df; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="ntuiy2le"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="5R42N7df" Date: Tue, 25 Nov 2025 12:50:08 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1764071409; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=DY7r9Cxa0yxiTtUEJHH+QVIBWnKQ+OLhnrHPaI1ZZmQ=; b=ntuiy2leAdUk5gy9/wa6Hw4BlemeM9nl3lTO705xp4FKTqQAvI7WsyyapUM7gCC+/oMgMC qG3xzTyw2YyYaTS46rigJBq6J77TjT4xEAjngwpP9wHqa7uJUKix9d5mqm8WEBYoHIkYdu ZUty2T/W5XzSL719R6Uoi0uMM+L/5ipyLxk2kwCnQTwrP1cva3kP/xfUIYktmUIGUPPIqi eqnC6ac83cfT6G+B+Ebm7o1J/oZ7fLpuO5yc7k3h7NPhO6B1upXR+8m8Ynl1CRwCQGXSPX 0YmKcWQhuJd5/raRbwuA89ndh7BmQt7Dbel3eUTt2DPHleQ7A9CYmtH/GljX2A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1764071409; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=DY7r9Cxa0yxiTtUEJHH+QVIBWnKQ+OLhnrHPaI1ZZmQ=; b=5R42N7dfi6l1dsCZ/OABuutwh8dUf349/xdi4S2MhNyRpHI6aCyI1/ULfLMxC/xiDc8RhI RznJhYw+5tTWKzDQ== From: "bigeasy@linutronix.de" To: Florian Bezdeka Cc: "Preclik, Tobias" , Frederic Weisbecker , "linux-rt-users@vger.kernel.org" , "Kiszka, Jan" Subject: Re: Control of IRQ Affinities from Userspace Message-ID: <20251125115008.-R5m5dX9@linutronix.de> References: <20251103155322.Aw9MSNYv@linutronix.de> <3cbc0cf5301350d87c03b7ceb646a3d7c549167b.camel@siemens.com> <6523960abaff2054ed25bf57b2a12e381f305a3e.camel@siemens.com> <20251111143456.YML0ggA7@linutronix.de> <20251124095919.V73BtuvW@linutronix.de> <387396748522d2279c3188e5c2b4345bc2211556.camel@siemens.com> Precedence: bulk X-Mailing-List: linux-rt-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: <387396748522d2279c3188e5c2b4345bc2211556.camel@siemens.com> On 2025-11-25 12:32:39 [+0100], Florian Bezdeka wrote: > > It seems that if you exclude certain CPUs from getting interrupt > > handling than it should work fine. Then the driver would only balance > > the interrupts among the CPUs that are left. >=20 > Sebastian, what exactly do you mean by "exclude certain CPUs from > getting interrupt handling"? I mean, that is what we do by configuring > the /proc//smp_affinity_list interface. Step #1 - figure out if isolcpus=3D is restricting the affinity of requested interrupts to housekeeping CPUs only Step #2 - Yes =3D> look for the matching knob in cgroup interface Knob found? - Yes =3D> Use knob. - No. =3D> Add knob. - No This should be added as it breaks the expectation of an isolated system. I *think* the driver should request as many interrupts as there are available CPUs in the system to handle them. The number of available CPUs/ CPU mask should be a configure knob by the user. Using the housekeeping CPUs as a default mask seems reasonable. The question is what should happen if the mask changes at runtime. Maybe a device needs to reconfigure, maybe just move the interrupt away. But this should also affect NOHZ_FULL workloads. > To sum up:=C2=A0 > - The IRQ balancing issue is not limited to a single driver / subsystem > - The managed IRQ infrastructure seems very "static" so insufficient for > this problem. In addition we would have to migrate all affected > drivers to the managed IRQ infrastructure first. >=20 > We would love to hear further thoughts / ideas / comments about this > problem. We're highly interested in fixing this issue properly. If the "managed IRQ infrastructure" would help here then why not. Maybe Frederic has some insight here. > Thanks for all the comments so far! >=20 > Florian Sebastian