From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 11E94C19F2B for ; Wed, 3 Aug 2022 22:45:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236764AbiHCWpC (ORCPT ); Wed, 3 Aug 2022 18:45:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33772 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229529AbiHCWpA (ORCPT ); Wed, 3 Aug 2022 18:45:00 -0400 Received: from alln-iport-4.cisco.com (alln-iport-4.cisco.com [173.37.142.91]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 063CB17A9E for ; Wed, 3 Aug 2022 15:44:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=cisco.com; i=@cisco.com; l=4612; q=dns/txt; s=iport; t=1659566699; x=1660776299; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=/432YnVJeuDkNOfsDeEGAMsx+rBO3FSvFcriqXL1K2E=; b=OqI81GfUMRfA4wIjv6BjHlbUt8Vj9C12+UBcjqCuBasmcd/Bsfw6ffhU 1tur255UxpIQk9iNktanqOKviBR3wew/crZNReKwuLK16yrr+dGhdHUit mXi54laFNh1qsu8cDrLuzCOHUsoOL/kSotwnwJwbvRMa2kpeXK8XPzldx A=; X-IronPort-AV: E=Sophos;i="5.93,214,1654560000"; d="scan'208";a="890430022" Received: from alln-core-1.cisco.com ([173.36.13.131]) by alln-iport-4.cisco.com with ESMTP/TLS/DHE-RSA-SEED-SHA; 03 Aug 2022 22:44:58 +0000 Received: from zorba (sjc-vpn6-26.cisco.com [10.21.120.26]) by alln-core-1.cisco.com (8.15.2/8.15.2) with ESMTPS id 273Miu1F021251 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Wed, 3 Aug 2022 22:44:57 GMT Date: Wed, 3 Aug 2022 15:44:55 -0700 From: Daniel Walker To: Marc Zyngier Cc: Thomas Gleixner , George Cherian , sgoutham@marvell.com, "BOBBY Liu (bobbliu)" , xe-linux-external@cisco.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] genirq: allow selection of number of sparse irqs Message-ID: <20220803224455.GA821407@zorba> References: <20220728030420.2279713-1-danielwa@cisco.com> <980a561ed87c5530aab2e2b067074862@kernel.org> <20220729182156.GS821407@zorba> <87wnbuc45y.wl-maz@kernel.org> <20220802223747.GX821407@zorba> <87sfmdbxvf.wl-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87sfmdbxvf.wl-maz@kernel.org> X-Auto-Response-Suppress: DR, OOF, AutoReply X-Outbound-SMTP-Client: 10.21.120.26, sjc-vpn6-26.cisco.com X-Outbound-Node: alln-core-1.cisco.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 03, 2022 at 08:16:20AM +0100, Marc Zyngier wrote: > On Tue, 02 Aug 2022 23:37:47 +0100, > Daniel Walker wrote: > > > > On Sat, Jul 30, 2022 at 10:59:05AM +0100, Marc Zyngier wrote: > > > > > > > > Marvell submitted a similar change, but non-selectable, about a > > > > month ago. > > > > > > Which wasn't really acceptable either. > > > > > > > > > > > The limitation prevents Cisco and Marvell hardware from > > > > functioning. I don't think we're well versed enough on the generic > > > > irq system to implement what your suggesting, even if we did Thomas > > > > would not likely accept it. > > > > > > I don't think you can speak for Thomas here. In my experience of > > > working with him, he's in general much more inclined to look at a > > > scalable, long term solution than at a point hack. Specially given > > > that we already use xarrays for MSIs. > > > > Your welcome make the attempt yourself, if you believe in it. > > The thing is, I don't need it, while you apparently do need a change > in the kernel. Do we ? A one line change is not hard to hold in our private tree, I'd rather not, but it's not hard. > > > > > > Your suggestion is more of a long term solution vs. our short term > > > > solution. > > > > > > Exactly. Experience shows that short term hacks are almost always a > > > bad idea and result in something that isn't maintainable. > > > > Thomas introduced the "hack" in c1ee626 in 2011. > > Yes. And it covers all the systems we care about so far. It is small, > fixed in size, and doesn't impose extra requirements on everyone else. > Your system changes the requirement, and it is the opportunity to > revisit an 11 year old decision. Who is "we" in the system cared about ? Are you suggesting there is a certain set of system Linux supports? > > It's more of a question of if someone has the time an and/or > > inclination to make the changes your requesting. > > No, it is about who has the need. You do, and nobody else does. Me, Cisco, and Marvell, and all of our customers isn't "nobody". > > Marvell and Cisco only require to increase the size and keep the > > status quo, and nothing is wrong with that. > > It is pretty wrong when it adds unneeded overhead on systems that > don't require this, and doesn't scale in the face of existing > architectures (let alone future ones). Distributions ship a single > kernel image, and would obviously select the largest possible value, > just to maximise perceived compatibility requirements. My ask is that > you don't inflict this on systems that do not need it. It adds no un-needed overhead to anyone. It defaults to the current size, if you make a config change you can increase it. There is no harm to other systems. > > > > > > I'm not wedded to any solution, we just need to relieve > > > > the limitation so our hardware starts working. I would imagine other > > > > companies have this issue, but I don't know which ones currently. > > > > > > This architecture has been in the wild for the best part of 10 years, > > > in Linux for 8 years, and nobody so far screamed because of this > > > perceived limitation. It would help if you described exactly what > > > breaks in your system, because just saying "give me more" is not > > > exactly helping (there are other limitations in the GICv3 ITS driver > > > that may bite you anyway). > > > > We need more irq lines because we have a lot of devices.. I suppose it's > > possible there's some defect in the kernel which eats up or wastes irq lines, > > but I don't think so. We have devices which use a lot of irq lines. > > > > > > I would rather to use an upstream solution verses holding the > > > > patches privately. I would suggest if this limitation would not be > > > > overcome for 3-4 releases the short term solution should be > > > > acceptable over that time frame to be replaced by something else > > > > after that. > > > > > > If you want to have an impact on the features being merged in the > > > upstream kernel, a good start would be to take feedback on board. > > > > We did that.. I updated the patch from Marvell's original to allow it to be > > selectable, this was requested by someone on this list. > > Well, I'm another "someone on the list" asking you to do better. You > are perfectly entitled to ignore me, and I'm just as entitled to voice > my opposition to your approach. Sure, We're all entitled to our opinions. Regardless of how terrible they may be. Daniel