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 825B0C19F2C for ; Tue, 2 Aug 2022 22:38:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236435AbiHBWiA (ORCPT ); Tue, 2 Aug 2022 18:38:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35314 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235175AbiHBWhw (ORCPT ); Tue, 2 Aug 2022 18:37:52 -0400 Received: from rcdn-iport-5.cisco.com (rcdn-iport-5.cisco.com [173.37.86.76]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3C7D217AA1 for ; Tue, 2 Aug 2022 15:37:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=cisco.com; i=@cisco.com; l=2671; q=dns/txt; s=iport; t=1659479871; x=1660689471; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=pKOnt7OBLC0Sl5DxaQljA8KzE5uazBS88utyntub/94=; b=T/0olTYMBocamuzarv239CBUCc348lWE6wE5vSXDGzHs6JU7CkaBRvWS gBPbP3gTk94gvsqpbjnyzhU7kcpRbrzh6/v41vcLWRg0xK/OnUiZ8yhOq b/l3g1sXZqLIs4eGiFmU3Cjugm90xYmTLJo4u6JbMi1fsmhGcvfPC7Rkc 8=; X-IronPort-AV: E=Sophos;i="5.91,230,1647302400"; d="scan'208";a="782774020" Received: from rcdn-core-2.cisco.com ([173.37.93.153]) by rcdn-iport-5.cisco.com with ESMTP/TLS/DHE-RSA-SEED-SHA; 02 Aug 2022 22:37:50 +0000 Received: from zorba (sjc-vpn6-436.cisco.com [10.21.121.180]) by rcdn-core-2.cisco.com (8.15.2/8.15.2) with ESMTPS id 272Mblld013996 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Tue, 2 Aug 2022 22:37:49 GMT Date: Tue, 2 Aug 2022 15:37:47 -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: <20220802223747.GX821407@zorba> References: <20220728030420.2279713-1-danielwa@cisco.com> <980a561ed87c5530aab2e2b067074862@kernel.org> <20220729182156.GS821407@zorba> <87wnbuc45y.wl-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87wnbuc45y.wl-maz@kernel.org> X-Auto-Response-Suppress: DR, OOF, AutoReply X-Outbound-SMTP-Client: 10.21.121.180, sjc-vpn6-436.cisco.com X-Outbound-Node: rcdn-core-2.cisco.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > 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. It's more of a question of if someone has the time an and/or inclination to make the changes your requesting. Marvell and Cisco only require to increase the size and keep the status quo, and nothing is wrong with that. > > 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. Daniel