From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qk1-f170.google.com (mail-qk1-f170.google.com [209.85.222.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 41861431E5B for ; Thu, 2 Jul 2026 00:16:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.222.170 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782951368; cv=none; b=nzGq5uR3oD3vhiNgU9+lVszJpt2/Noi0V3PiUgWJMfbqEtirtxoNRUU6TTluxMcv5Vwz7yDwKAdF3jJrAA4rzGE1s2Iq3bWBF04DFlwSVN71UMZDmndmpySNTVCJuGLIHMUe6z4wQxzT46mRltkdtATmAq92en6nt95p0PUe0us= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782951368; c=relaxed/simple; bh=iBCjZsNh3SRSbwVqKwjZlanD4uaJXSQ+DBZTbOJ2auQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=kuq26g8F5jaJjGXRiBbkrMp4ttZwNstuZ+k5nSWhhW9uB/eEgzN363YoQ5UfT2E8uLKG38cDDN9H0b9nDztROJstlyZYZhvXjQ/nSipVh7dcC7XhM71v0LzloFMIVrpt9h0yxZNxkh9yM9X7arsNdZcnLLzeYoGuoqdJX/Y1eKo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ziepe.ca; spf=pass smtp.mailfrom=ziepe.ca; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b=iXEQQ20I; arc=none smtp.client-ip=209.85.222.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ziepe.ca Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ziepe.ca Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b="iXEQQ20I" Received: by mail-qk1-f170.google.com with SMTP id af79cd13be357-92e53581361so70423485a.1 for ; Wed, 01 Jul 2026 17:16:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; t=1782951365; x=1783556165; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=SpRDP2ezaOKhK6W6X5fU8vOvQc+ihhDBQ+gm9ShOsoo=; b=iXEQQ20IOXNIoMHqosBhpL7RZopWX9QKyHU9EQ9/zEA08o3xnWOWHsahgJzLtpkBXU WM1XtUWVrkQYjDPbc0P+G5aofTRsZT7njaaJ0yyWIHj4yjKrKWRcOacFiGB99DJx0Ekg t08wAy+NbfzAj6iZ2q+vifWqpV0vMhE2L24uacozgNwjIm+M5shKC9mH8PCEbi89mw1l C/2cZrX5DHO6z1+n+KJxWUnman1vgKjokhkeYqhpgogs9A3cyTeUdaYPCS+wsHfBRaVN xibS6CfdUZDmzCwqJAQCrjTVZvsI2ENDGWFTV6kQ0rBstbmJZaqfq7mjzbG2UVoODH4j ZgEw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782951365; x=1783556165; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=SpRDP2ezaOKhK6W6X5fU8vOvQc+ihhDBQ+gm9ShOsoo=; b=jWj53BikXpPToZ6G4jrXiUsY/Z/jJnn7AyHdr6Jh9cN6pEd6/md2FkbAbjqt3aa0BN z6WREHYF/EhI/BQjLkQGz2FuA3kaT3e4RIgmaZYuhmzC32dQJvz7D7oNxFR+FQzU//iH 53B5rLi+ZhuM1VzD+VrBsKMAZGlWDvvIXDtFeF/0zjafRhtSfoOsdFjqN/zPxOKa+vkj PDpmqSWF/7YkNUPGZws+T44p5U/eyYZrH+qkXOiOBJJEqToyHPKAPNeMROUR+R1NDI3+ kp25AeZ9X0rHR7bfTcQH4jW/tqvtBKzWpaAtuIUcaioxCAmYeyswn5jyEiM4JX61y9cy rjDg== X-Forwarded-Encrypted: i=1; AFNElJ/FRWElArNqvQx5IdsC9XgIsCY3b+lh4FmamrhRQn1kKHeZvWxOo2ri/cXT4ouUJzPO7zDJ/GyP3ZFP3Os=@vger.kernel.org X-Gm-Message-State: AOJu0YwIYI1BV0RQVNNS6XYv87/yhQfP4hxyEG43tT1O9UV84Iwww4DA +WUPhA21j5dD3imwB3uAXRnddkvcvLIUh9SDYPwr2dE4l63yer/2+v1CF5lQJa3wJuUjjLheM/V BvGbX X-Gm-Gg: AfdE7cmX2zFWJYICIMa0ZUjnY9b5jrZJm0zjO4/qnJ2lmHGLLA+vzRjceOLTXMSkmnA PSUAmeoRv7SBTMNLTap2v9EmgtI11335y/jb1WkpwPeNzjHYzz68QyVU86cf3ODvyXpRKvP/N3W /LmNYeGe3kSM59kAWJDzJxnNg5QN5OQ6ef5EiKP2zlhL8F7pqjCfcuyCBsjm/XHSZRZJMAlGGzY uGkNb9t7HWmDCsSrjxlA7y91tHtx8iUom0hpYiLUxQkCq7zb6B/ZvfqMJMP9FvdDebgapiBh4km qdFYIKA2QY57apDaDZLMqlfIsxkFS5FcVl8CZKc8KRUem71+NBiT6qF0oPsPznxGpyMS4aJrO6y oAq6YmEWaepoNIErNbO2kmN/WJqh4NG0hevvo0IN4gBS8tJpb0sgR4+AfmbOj0FssnIZhw9rDkR GDir+MtApHTS4qcKpUlW00U/DdsCQWJPLt/DK1vJhBBZg8cleFmZlKwSZmqYGWBZG5p7o= X-Received: by 2002:a05:620a:4016:b0:915:8f76:7ffa with SMTP id af79cd13be357-92e782c6315mr515090585a.45.1782951365126; Wed, 01 Jul 2026 17:16:05 -0700 (PDT) Received: from ziepe.ca (crbknf0213w-47-54-130-67.pppoe-dynamic.high-speed.nl.bellaliant.net. [47.54.130.67]) by smtp.gmail.com with ESMTPSA id af79cd13be357-92e80040ff1sm81033885a.21.2026.07.01.17.16.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jul 2026 17:16:04 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1wf563-00000004cjY-2WuA; Wed, 01 Jul 2026 21:16:03 -0300 Date: Wed, 1 Jul 2026 21:16:03 -0300 From: Jason Gunthorpe To: "Kiryl Shutsemau (Meta)" Cc: Will Deacon , Robin Murphy , Joerg Roedel , Nicolin Chen , Kyle McMartin , Breno Leitao , Usama Arif , linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] iommu/arm-smmu-v3: Shrink command/event/PRI queues in kdump kernel Message-ID: <20260702001603.GN7525@ziepe.ca> References: <20260701154528.768976-1-kas@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260701154528.768976-1-kas@kernel.org> On Wed, Jul 01, 2026 at 04:45:28PM +0100, Kiryl Shutsemau (Meta) wrote: > The command, event and PRI queues are sized from the maxima the hardware > advertises in IDR1, which can be several megabytes each. On systems with > many SMMUv3 instances that cost is paid per instance and adds up to tens > of megabytes of coherent DMA in the capture kernel. > > A kdump capture kernel runs from a small crashkernel reservation and only > has to drive the few devices used to save the dump, so deep queues serve > no purpose. The queues carry invalidation commands and fault records, not > DMA data, so dump throughput is unaffected; a shallower queue only bounds > how many commands may be in flight before a sync, which does not matter for > the capture kernel's small device count and modest I/O. > > Clamp every queue to a single page when is_kdump_kernel() is true. Doing > it in arm_smmu_init_one_queue() covers the command, event and PRI queues > in one place. The command queue still holds at least one batch plus a sync > (256 entries on a 4K-page kernel, well above CMDQ_BATCH_ENTRIES), so > command batching keeps working. > > Suggested-by: Kyle McMartin > Signed-off-by: Kiryl Shutsemau (Meta) > --- > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) Make sense to me > + if (is_kdump_kernel()) { > + u32 ent_sz_shift = ilog2(dwords) + 3; > + > + q->llq.max_n_shift = min_t(u32, q->llq.max_n_shift, > + PAGE_SHIFT - ent_sz_shift); I saw lately many people saying you should not use min_t, why is it needed here? Jason