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 X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7D743C432C0 for ; Tue, 3 Dec 2019 11:50:39 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 4E85F2073C for ; Tue, 3 Dec 2019 11:50:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="rTLILhLf"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="llxNGju3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4E85F2073C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=cqbxTHOfJ4hXErkuYcte8cz3bNczFsSS1hkvTuMmi1k=; b=rTLILhLfVGMbsG qRWXEmpM2ogWRAOEK5NECsMb+2302O/9vu+nQzvyKWvF3x3x/6Ic6f3XI3vRGc+aGFogJtmzrAaZx mvUgl0CSBWFdmgSbbGWqJPGtb1SMmourOIp+T6iiPvm1x/iTaLW22yAqqp2Rx10gG0cP4jYaYep7r RTNrimlERD7j8aspKp8DRjYljTLjstJBE8skZn1JOkffuIDKP12sdQsJuePD4Ai0/whZKOcZyk9Nu wkn+ByRTlLRYnmwT6BvYUhlDsVr0iZdihYyePT/LXbV/jDoEG4eJd7bIvjkvk57H7XWpYpmIsim6e Gj59CxEFFJjGRsCUR/ew==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1ic6hP-0004Sn-Fs; Tue, 03 Dec 2019 11:50:35 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1ic6h4-00043t-Oy for linux-nvme@lists.infradead.org; Tue, 03 Dec 2019 11:50:18 +0000 Received: from C02WT3WMHTD6.lpcnextlight.net (rap-us.hgst.com [199.255.44.250]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7AD3620684; Tue, 3 Dec 2019 11:50:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575373814; bh=XS++FmgaW2NMEKh9y3FRpOPiq7KQ/LeEF1ki4nUG4VE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=llxNGju3r2ofZlhck7zId16xJjiAHuuDyy0AukkIYJ88MtcmAAGl9T1vqZu4WL66k D3ZMLwrXUpNLbyp/Ofhqzy9WYaOWe6PoOqxxV/ZyuHCJZRIR1DL02sGENNLLH9Z/Ph vbUuqXrRk7HNk8nlJZWMWuMJpfh0OupdD2DCZAbM= Date: Tue, 3 Dec 2019 04:50:06 -0700 From: Keith Busch To: Christoph Hellwig Subject: Re: [RFC PATCH 1/3] nvme/pci: Poll the cq in the primary irq handler Message-ID: <20191203115006.GB86476@C02WT3WMHTD6.lpcnextlight.net> References: <20191202222206.2225-1-kbusch@kernel.org> <20191202222206.2225-2-kbusch@kernel.org> <20191203075046.GF23881@lst.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20191203075046.GF23881@lst.de> User-Agent: Mutt/1.12.1 (2019-06-15) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191203_035014_918690_9AE20C41 X-CRM114-Status: GOOD ( 18.05 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: bigeasy@linutronix.de, tglx@linutronix.de, sagi@grimberg.me, linux-nvme@lists.infradead.org, ming.lei@redhat.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Tue, Dec 03, 2019 at 08:50:46AM +0100, Christoph Hellwig wrote: > On Tue, Dec 03, 2019 at 07:22:04AM +0900, Keith Busch wrote: > > The nvme threaded interrupt handler reduces CPU time spent in hard irq > > context, but waking it increases latency for low queue depth workloads. > > > > Poll the completion queue once from the primary handler and wake the > > thread only if more completions remain after. > > How is this going to work with -rt, which wants to run all actual > interrupt work in the irq thread? That just has the primary and the bottom half run as threads. This patch just avoids a context switch for shallow workloads whether use -rt or not. > > Since there is a window > > of time where the threaded and primary handlers may run simultaneously, > > add a new nvmeq flag so that the two can synchronize which owns processing > > the queue. > > If the above scheme is something that the irq subsystem maintainers are > fine with I think we need to lift that synchronization into the core > irq code instead of open coding it in drivers. It's not generally applicable to all drivers, so it'd have to be an opt-in. I think IRQF_ONESHOT pretty much captures the same idea, though. > But I'd love to understand what kind of performance this split scheme > gives us to start with. Do you have any numbers? I do have a little bit of data. On a queue-depth 1 test, returning IRQ_WAKE_THREAD adds just under 1usec latency compared to completing in the primary handler. That's about 10% for some of the faster devices out there. _______________________________________________ linux-nvme mailing list linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme