From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 1F74F2F7EF9; Thu, 6 Aug 2026 13:00:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786021238; cv=none; b=AnKO2MnW0sJQXaIHr+zAfkgE7SgNrb19Yoa4751G83txSU1TTMwlmC2uOL9sMNjrLxiF2U+lLEtgaTKEdNvFdenX3O3q0MOukq7Vc6/9PfiHB+0vwXahklrv1DwET6TaFffaveBXr7WT1efFNAMWcCbqRu8PsJnzWoBiBfTetds= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786021238; c=relaxed/simple; bh=VnKGLBjKLa1ViHCd9+00d1v2tcASVXRCUxALBKBo9lE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rVW4xv2U2Jm20jtbRruoWHj9mnMV56s3zFqnXg7gnMfMV22Fu9Fi6ogA75N0HkH0QumFnYqycIpERO03lRRndLrKx9RmTSSUi1rAZrQ1aCbSInWcj35uDVdg8giZiu4vwmjr5VMDioeAkuOJTiV5bJ74nzE4E1zfgrM1SmidlmU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=a86oeqp4; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="a86oeqp4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 52E551F000E9; Thu, 6 Aug 2026 13:00:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786021234; bh=mW/OuZ6mDAqPwiWKjJo6a74gpl79w+/96YfJnOrsAnE=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=a86oeqp4RR3VHaJpTt4R9aiSI/uw/jdngWhLSd2xywYg+BiVfBYpQynxbLq654MRU O0eRadyZulK73laweC/FpAtNgiIJQgHJdJFnaHTBjNnrblMOj60N2M91wUg+g7OVJC B4v0KVk4P2V+RwWdSjexPi1bzKlWMRWkXQW82wlZvdWz78EIedX7kjxAroGNoiUiXc 8UURMYbrxTSFLK0DK7TKkezyaLdUnMTb3RgxoF0XMEi71Vf5TPw1FXBvR0dTbh/aq6 jBlYPIfOnCUn+I37wjoXKkbxkUDieYBRJQdFx3yC3uPNcmDt8xci5B52/40FIT3qM0 JoNnwfn81OOKQ== Date: Thu, 6 Aug 2026 14:00:28 +0100 From: Will Deacon To: Nicolin Chen Cc: Jason Gunthorpe , Kiryl Shutsemau , Robin Murphy , Joerg Roedel , Pranjal Shrivastava , Breno Leitao , Kyle McMartin , Usama Arif , linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] iommu/arm-smmu-v3: Shrink command/event/PRI queues in kdump kernel Message-ID: References: <20260706084708.8072-1-kas@kernel.org> <20260804141704.GB27883@nvidia.com> <20260804161918.GG27883@nvidia.com> <20260804165905.GH27883@nvidia.com> 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: On Tue, Aug 04, 2026 at 10:39:13AM -0700, Nicolin Chen wrote: > On Tue, Aug 04, 2026 at 01:59:05PM -0300, Jason Gunthorpe wrote: > > On Tue, Aug 04, 2026 at 09:45:01AM -0700, Nicolin Chen wrote: > > > On Tue, Aug 04, 2026 at 01:19:18PM -0300, Jason Gunthorpe wrote: > > > > On Tue, Aug 04, 2026 at 09:04:32AM -0700, Nicolin Chen wrote: > > > > > On Tue, Aug 04, 2026 at 11:17:04AM -0300, Jason Gunthorpe wrote: > > > > > > On Tue, Aug 04, 2026 at 03:02:46PM +0100, Will Deacon wrote: > > > > > > > > Would skipping their allocation when is_kdump_kernel() be acceptable on > > > > > > > > its own, or would you rather see it done differently? > > > > > > > > > > > > > > With Nicolin's patch, we can just avoid allocating the priq and the evtq > > > > > > > entirely in the kdump case. We can then add a cmdline option to control > > > > > > > the maximum size of the cmdq, which is useful regardless of kdump. > > > > > > > > > > > > I would still prefer kdump do this re-sizing automatically, even if we > > > > > > do add a commandline. It makes it easire to deploy than having to know > > > > > > secret command lines :\ > > > > > > > > > > > > So functionally I still think this patch is fine, though yes it points > > > > > > out more things in Nicolin's work too. > > > > > > > > > > I will send a v10 of mine, to skip the EVTQ/PRIQ allocations. > > > > > > > > I think Robin's point is to structure the v10 so you introduce a bunch > > > > of tunables, including something like 0 size to disable a feature. > > > > > > > > Then have kdump default those tunables to the right thing > > > > > > But in kdump, EVTQ/PRIQ are disabled, so my series should have > > > skipped their allocations regardless of the tunables. > > > > > > So, I think the tunables can be done in a separate series. And > > > its use case might not be confined to kdump? > > > > I think the ask is to do the tunables first and change your series to > > default the tunables instead of doing direct kdump overrides. > > You mean the driver can override the tunables to 0 in kdump mode, > right? > > Well, we are skipping a lot of things in kdump mode already; it's > a very small change to skip EVTQ/PRIQ even without the tunables. > > If Will prefers this merging sequence, I wouldn't mind changing my > series to overriding the tunables. I was thinking that the tunable would only apply to the cmdq. We can extend it later if necessary, but since we're not going to enable the evtq/priq in kdump mode at all, I don't think we need tunables for those atm. I probably wouldn't make a size of 0 disable the queue, either. Have a minimum size of a page or something like that. Will