From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 A19F9366; Tue, 18 Mar 2025 07:57:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742284640; cv=none; b=ZXsQFwg+ribz868YyhlU0nW3mg71dgwjwF6RQgErayccct6Hn0d85rjch+YeIBTkftmXxB+nZCYNuONZR5yuA5LRtWxmetL8Iqcbgd8BxVAamIyy+gwp5PzhQ5lWDujGCtbmDAW86H9RzaLUhnEL93VrjX74C/Ilgf9flIU+3iQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742284640; c=relaxed/simple; bh=Iz4pqOI235ydHMfcg0FHxBlUlROBEcfWRt7n7cVLelM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YvscSlFMVm8omzDqA1+LivnzHbcdEOFwoZIqmknd790EIfWfzrnPBup8qJhwhVJLXHjdbDi71l2ZfSqfPZy4764bGeP1wWFaX43oTgiewmtl/K1JOOa8TQ3ebNbQr5fvC8cmAfFW7DhYhDg2ITThNip7PY7WFQgYa+X5KimX69s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=akwP3jJv; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="akwP3jJv" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=tLs/bxImix0heMMO25L/sr+bZhE4jHdYqj5az0Wt+Ug=; b=akwP3jJvOF2A9MTOiAacMLR609 oTvNtg30xrh+ZQiPr4PvY2Olryg/pl8i8C4KSgl9x0VCkLnd1mZpXKYC4WmhWuDRbRhhaJa66s8ol z1I34KSc29fMB52cwifBVW4OVbGochoGb7G1BkRrHIqs0enFBAONF/l8NddSZIb8tcKAMeTf2VjVE DbuXUVGjWkT7eDmOcxz26WO3CzFAaIwX5z1cL7leWyJfEygHnkCLd60ILMwpHd3EZndbTnXBGMxS/ yoXojB6c3Go9T1ptR9VtUFcRzYmUOD1ty4FaL2Kxdk632IBO+3wPv/TzuSsNZC0hAHvet1do2MdoY nergSn3g==; Received: from hch by bombadil.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tuRp7-000000053eT-0UoO; Tue, 18 Mar 2025 07:57:17 +0000 Date: Tue, 18 Mar 2025 00:57:17 -0700 From: Christoph Hellwig To: Dave Chinner Cc: Mikulas Patocka , Ming Lei , Christoph Hellwig , Jens Axboe , Jooyung Han , Alasdair Kergon , Mike Snitzer , Heinz Mauelshagen , zkabelac@redhat.com, dm-devel@lists.linux.dev, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org Subject: Re: [PATCH] the dm-loop target Message-ID: References: <81b037c8-8fea-2d4c-0baf-d9aa18835063@redhat.com> <7b8b8a24-f36b-d213-cca1-d8857b6aca02@redhat.com> Precedence: bulk X-Mailing-List: io-uring@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: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Tue, Mar 18, 2025 at 03:27:48PM +1100, Dave Chinner wrote: > Yes, NOWAIT may then add an incremental performance improvement on > top for optimal layout cases, but I'm still not yet convinced that > it is a generally applicable loop device optimisation that everyone > wants to always enable due to the potential for 100% NOWAIT > submission failure on any given loop device..... Yes, I think this is a really good first step: 1) switch loop to use a per-command work_item unconditionally, which also has the nice effect that it cleans up the horrible mess of the per-blkcg workers. (note that this is what the nvmet file backend has always done with good result) 2) look into NOWAIT submission, especially for reads this should be a clear winner and probaby done unconditionally. For writes it might be a bit of a tradeoff if we expect the writes to allocate a lot, so we might want some kind of tunable for it.