From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 8E88F134B3 for ; Mon, 26 Jun 2023 18:22:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 09625C433C0; Mon, 26 Jun 2023 18:22:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1687803741; bh=hqxEYoAmnMDCGmJl4aQkAxDCHg7P7SJ/x/QzYFVMjKg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=HG8UTn1zY3S8LYtYbmc/WQltupvQ8CNd/DVnpJqDaLqt5/myA+NL9YvrLscGkNa+U kf0KhfmQJnxm9NREBxfwSMMXTTN/2cNzODoqtcjJGWdSXB9rnEtCJ2K+hrtLWwq5Br UVTVPhSAuK9cOSU5de//hOo+jSA7+wtJ8w9sZKos= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Costa Sapuntzakis , Randy Jennings , Uday Shankar , Hannes Reinecke , Sagi Grimberg , Christoph Hellwig , Keith Busch , Sasha Levin Subject: [PATCH 6.3 162/199] nvme: double KA polling frequency to avoid KATO with TBKAS on Date: Mon, 26 Jun 2023 20:11:08 +0200 Message-ID: <20230626180812.777669435@linuxfoundation.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230626180805.643662628@linuxfoundation.org> References: <20230626180805.643662628@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Uday Shankar [ Upstream commit ea4d453b9ec9ea279c39744cd0ecb47ef48ede35 ] With TBKAS on, the completion of one command can defer sending a keep alive for up to twice the delay between successive runs of nvme_keep_alive_work. The current delay of KATO / 2 thus makes it possible for one command to defer sending a keep alive for up to KATO, which can result in the controller detecting a KATO. The following trace demonstrates the issue, taking KATO = 8 for simplicity: 1. t = 0: run nvme_keep_alive_work, no keep-alive sent 2. t = ε: I/O completion seen, set comp_seen = true 3. t = 4: run nvme_keep_alive_work, see comp_seen == true, skip sending keep-alive, set comp_seen = false 4. t = 8: run nvme_keep_alive_work, see comp_seen == false, send a keep-alive command. Here, there is a delay of 8 - ε between receiving a command completion and sending the next command. With ε small, the controller is likely to detect a keep alive timeout. Fix this by running nvme_keep_alive_work with a delay of KATO / 4 whenever TBKAS is on. Going through the above trace now gives us a worst-case delay of 4 - ε, which is in line with the recommendation of sending a command every KATO / 2 in the NVMe specification. Reported-by: Costa Sapuntzakis Reported-by: Randy Jennings Signed-off-by: Uday Shankar Reviewed-by: Hannes Reinecke Reviewed-by: Sagi Grimberg Reviewed-by: Christoph Hellwig Signed-off-by: Keith Busch Signed-off-by: Sasha Levin --- drivers/nvme/host/core.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c index f12109230dc8d..3838a6622c34b 100644 --- a/drivers/nvme/host/core.c +++ b/drivers/nvme/host/core.c @@ -1163,9 +1163,25 @@ EXPORT_SYMBOL_NS_GPL(nvme_passthru_end, NVME_TARGET_PASSTHRU); * The host should send Keep Alive commands at half of the Keep Alive Timeout * accounting for transport roundtrip times [..]. */ +static unsigned long nvme_keep_alive_work_period(struct nvme_ctrl *ctrl) +{ + unsigned long delay = ctrl->kato * HZ / 2; + + /* + * When using Traffic Based Keep Alive, we need to run + * nvme_keep_alive_work at twice the normal frequency, as one + * command completion can postpone sending a keep alive command + * by up to twice the delay between runs. + */ + if (ctrl->ctratt & NVME_CTRL_ATTR_TBKAS) + delay /= 2; + return delay; +} + static void nvme_queue_keep_alive_work(struct nvme_ctrl *ctrl) { - queue_delayed_work(nvme_wq, &ctrl->ka_work, ctrl->kato * HZ / 2); + queue_delayed_work(nvme_wq, &ctrl->ka_work, + nvme_keep_alive_work_period(ctrl)); } static enum rq_end_io_ret nvme_keep_alive_end_io(struct request *rq, -- 2.39.2