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 E034B30E828; Mon, 25 May 2026 05:17:37 +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=1779686262; cv=none; b=t/tHOTw55yI8qPeR5yLo/2904g7bLnThCXo7D1ry0CnEeaKwpQHeb9v686y4WiP53uUAhHKQqPeNO/nvgr2bo2RwdON9KMeWoffwzBJekEjnSZFoOzTcqRtWOm6vSJ9GFJx2x3Wj7xgF4OyhCjjJRL1lMHeqEPzDlmaUbGO/lPQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779686262; c=relaxed/simple; bh=ZhbE90TpM/1he8VU/w83v8tewOyDUveEm8gaa9VDpag=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YIzlp3L/s+5csCkS6FSPZbZ9NLsyusqahWD1Ec63UILodhwHBPLKcGkpQOJtjXAupIEfPtBwntVX/AAn33o83FqMnCliG7CCVYzemERIJldbYrF8BKHFbww1xSkDC6WuIlGSEHNSUPep3Aym6zFIkcQ0K1tN6XoJ4NVDKegp9yA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (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=GLm05S0P; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (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="GLm05S0P" 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=WGFWPzw6+sfQbAaiqeC7ZcWGmRnj56UaqVBKUeVEioE=; b=GLm05S0PC4mGsmC79PM1H00V2a bZDM/XiGMekJuKe97X9xAfLAxDV/rMnkNBSDLgOZ3/ylKMgBZdwvLnffl2mFwdPae5Q+832q8eqiB BSRO5uuokBeK+XKYCbNp2TAradZX7/IYOlyE2dUKOSNqab98xY6Qdaud8IsLYU27ATb/gdS6t78Bu tCIHrhr/FJoo0DS5knx1zdVXph3SrOTV2LEGGQrLXgMbCMJFJKwVz1EnNw+cWVNuw/i6fzUb4u8d4 tUUzJS7eFimHgrCaY6/KE+eBembed6MlM4geLu5MhUeKky4EYQEtS8jSmHMbMFXhxsTUE5249dP2i niEzrsPg==; Received: from hch by bombadil.infradead.org with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1wRNgv-0000000GJGp-3yPC; Mon, 25 May 2026 05:17:29 +0000 Date: Sun, 24 May 2026 22:17:29 -0700 From: Christoph Hellwig To: Tal Zussman Cc: Christoph Hellwig , Jens Axboe , "Matthew Wilcox (Oracle)" , Christian Brauner , "Darrick J. Wong" , Carlos Maiolino , Alexander Viro , Jan Kara , Dave Chinner , Bart Van Assche , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Gao Xiang Subject: Re: [PATCH v6 1/4] block: add task-context bio completion infrastructure Message-ID: References: <20260514-blk-dontcache-v6-0-782e2fa7477b@columbia.edu> <20260514-blk-dontcache-v6-1-782e2fa7477b@columbia.edu> Precedence: bulk X-Mailing-List: linux-block@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 Fri, May 22, 2026 at 06:47:43PM -0400, Tal Zussman wrote: > > But this 1-jiffie delay also means we unconditionally increase > > completion latency, which feels like a bad idea. Do you have any > > measurements that show where it does benefit? Note that queing work > > already often has very measurable latency on it's own. This also > > directly contradics the erofs experience that even went to a RT > > thread to reduce the latency. > > I added this per Dave's feedback on v4, where he noted that XFS inodegc > uses a delayed work item to avoid context switch storms. There's only a > delay for the first bio in a batch to complete, as we only delay when the > list is empty. I'll run some experiments and measure context switches, > completion latency, etc. to see if this is necessary. The difference is that XFS inodegc is not latency bound. Most of the time no one cares if it is delayed a bit, in the cases where someone cares we explicitly flush the queues. I/O completion on the other hand is something where users very much care about latency.