From patchwork Thu Mar 7 22:25:09 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Michal Schmidt X-Patchwork-Id: 13586318 X-Patchwork-Delegate: kuba@kernel.org Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 1D02D1369A6 for ; Thu, 7 Mar 2024 22:25:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709850334; cv=none; b=ieS49BRkAoHiYLNbcmkSKsmAX5wBSZ+oODyQmM6a6IhC+b93XT2cvgwG2Rd4AkQwU7zElFxf4gmIQ2dZxaD67DM+iF3NICKXZ5odFkL7mYh5+ZUwqInerssnqpB5kqSuS/lskx3Z48P8X4lUvqN6O3qbALFogkcGRTRVZhrte9Q= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709850334; c=relaxed/simple; bh=KQcQreIf3KdOicPjO9dHk2ak2UkMoJ1DPP2sRE6UVuI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=oaotTQLS/2qcq/ubERnv39QwD2Y+/N14xsN5ez16v2sw3QyEHER34K32Lh3V10Crg9G4rpzJJRLCDy3+6gTHU0+MoJN0kV7+kczAWJFC67zVaksAE6XMc8ClcbwPCW28xQ4ZZtcJprPbW4EVTJfOva59fe5J3mOjB90WqArHWS8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=IJ4wH4Dq; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="IJ4wH4Dq" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1709850332; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fCashlk1j8zw2cFRgsBziq5vcTt9z8cZj/gEJ/sKkLE=; b=IJ4wH4Dq8fIJQPlAS53mEjwdqbJ2ageB3f1utlL2YnKXv16ULtYwC0V99+D7BRBRNmcgq8 2YMqS2Snr2bB+Rdd4k4FNIdZb38WVb2IBjovPv4AUf14no8KDXTwsfC613MRA+FYNK/j2g FSCVgITT+JkOZ5uDNbIwfHO5bIK/0i4= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-680-UAZAAPuCOCuz79uZczs4Pw-1; Thu, 07 Mar 2024 17:25:27 -0500 X-MC-Unique: UAZAAPuCOCuz79uZczs4Pw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7639B800264; Thu, 7 Mar 2024 22:25:26 +0000 (UTC) Received: from toolbox.redhat.com (unknown [10.45.224.83]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8A5951C060D6; Thu, 7 Mar 2024 22:25:24 +0000 (UTC) From: Michal Schmidt To: intel-wired-lan@lists.osuosl.org Cc: netdev@vger.kernel.org, Jacob Keller , Jakub Kicinski , Jiri Pirko , Jesse Brandeburg , Arkadiusz Kubalewski , Karol Kolacinski Subject: [PATCH net-next v3 2/3] ice: avoid the PTP hardware semaphore in gettimex64 path Date: Thu, 7 Mar 2024 23:25:09 +0100 Message-ID: <20240307222510.53654-3-mschmidt@redhat.com> In-Reply-To: <20240307222510.53654-1-mschmidt@redhat.com> References: <20240307222510.53654-1-mschmidt@redhat.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 X-Patchwork-Delegate: kuba@kernel.org The PTP hardware semaphore (PFTSYN_SEM) is used to synchronize operations that program the PTP timers. The operations involve issuing commands to the sideband queue. The E810 does not have a hardware sideband queue, so the admin queue is used. The admin queue is slow. I have observed delays in hundreds of milliseconds waiting for ice_sq_done. When phc2sys reads the time from the ice PTP clock and PFTSYN_SEM is held by a task performing one of the slow operations, ice_ptp_lock can easily time out. phc2sys gets -EBUSY and the kernel prints: ice 0000:XX:YY.0: PTP failed to get time These messages appear once every few seconds, causing log spam. The E810 datasheet recommends an algorithm for reading the upper 64 bits of the GLTSYN_TIME register. It matches what's implemented in ice_ptp_read_src_clk_reg. It is robust against wrap-around, but not necessarily against the concurrent setting of the register (with GLTSYN_CMD_{INIT,ADJ}_TIME commands). Perhaps that's why ice_ptp_gettimex64 also takes PFTSYN_SEM. The race with time setters can be prevented without relying on the PTP hardware semaphore. Using the "ice_adapter" from the previous patch, we can have a common spinlock for the PFs that share the clock hardware. It will protect the reading and writing to the GLTSYN_TIME register. The writing is performed indirectly, by the hardware, as a result of the driver writing GLTSYN_CMD_SYNC in ice_ptp_exec_tmr_cmd. I wasn't sure if the ice_flush there is enough to make sure GLTSYN_TIME has been updated, but it works well in my testing. My test code can be seen here: https://gitlab.com/mschmidt2/linux/-/commits/ice-ptp-host-side-lock-9 It consists of: - kernel threads reading the time in a busy loop and looking at the deltas between consecutive values, reporting new maxima. - a shell script that sets the time repeatedly; - a bpftrace probe to produce a histogram of the measured deltas. Without the spinlock ptp_gltsyn_time_lock, it is easy to see tearing. Deltas in the [2G, 4G) range appear in the histograms. With the spinlock added, there is no tearing and the biggest delta I saw was in the range [1M, 2M), that is under 2 ms. Signed-off-by: Michal Schmidt --- drivers/net/ethernet/intel/ice/ice_adapter.c | 2 ++ drivers/net/ethernet/intel/ice/ice_adapter.h | 6 ++++++ drivers/net/ethernet/intel/ice/ice_ptp.c | 8 +------- drivers/net/ethernet/intel/ice/ice_ptp_hw.c | 3 +++ 4 files changed, 12 insertions(+), 7 deletions(-) diff --git a/drivers/net/ethernet/intel/ice/ice_adapter.c b/drivers/net/ethernet/intel/ice/ice_adapter.c index 6b9eeba6edf7..bd5f346bc603 100644 --- a/drivers/net/ethernet/intel/ice/ice_adapter.c +++ b/drivers/net/ethernet/intel/ice/ice_adapter.c @@ -5,6 +5,7 @@ #include #include #include +#include #include #include "ice_adapter.h" @@ -28,6 +29,7 @@ static struct ice_adapter *ice_adapter_new(void) if (!adapter) return NULL; + spin_lock_init(&adapter->ptp_gltsyn_time_lock); refcount_set(&adapter->refcount, 1); return adapter; diff --git a/drivers/net/ethernet/intel/ice/ice_adapter.h b/drivers/net/ethernet/intel/ice/ice_adapter.h index cb5a02eb24c1..9d11014ec02f 100644 --- a/drivers/net/ethernet/intel/ice/ice_adapter.h +++ b/drivers/net/ethernet/intel/ice/ice_adapter.h @@ -4,15 +4,21 @@ #ifndef _ICE_ADAPTER_H_ #define _ICE_ADAPTER_H_ +#include #include struct pci_dev; /** * struct ice_adapter - PCI adapter resources shared across PFs + * @ptp_gltsyn_time_lock: Spinlock protecting access to the GLTSYN_TIME + * register of the PTP clock. * @refcount: Reference count. struct ice_pf objects hold the references. */ struct ice_adapter { + /* For access to the GLTSYN_TIME register */ + spinlock_t ptp_gltsyn_time_lock; + refcount_t refcount; }; diff --git a/drivers/net/ethernet/intel/ice/ice_ptp.c b/drivers/net/ethernet/intel/ice/ice_ptp.c index c11eba07283c..0875f37add78 100644 --- a/drivers/net/ethernet/intel/ice/ice_ptp.c +++ b/drivers/net/ethernet/intel/ice/ice_ptp.c @@ -374,6 +374,7 @@ ice_ptp_read_src_clk_reg(struct ice_pf *pf, struct ptp_system_timestamp *sts) u8 tmr_idx; tmr_idx = ice_get_ptp_src_clock_index(hw); + guard(spinlock)(&pf->adapter->ptp_gltsyn_time_lock); /* Read the system timestamp pre PHC read */ ptp_read_system_prets(sts); @@ -1925,15 +1926,8 @@ ice_ptp_gettimex64(struct ptp_clock_info *info, struct timespec64 *ts, struct ptp_system_timestamp *sts) { struct ice_pf *pf = ptp_info_to_pf(info); - struct ice_hw *hw = &pf->hw; - - if (!ice_ptp_lock(hw)) { - dev_err(ice_pf_to_dev(pf), "PTP failed to get time\n"); - return -EBUSY; - } ice_ptp_read_time(pf, ts, sts); - ice_ptp_unlock(hw); return 0; } diff --git a/drivers/net/ethernet/intel/ice/ice_ptp_hw.c b/drivers/net/ethernet/intel/ice/ice_ptp_hw.c index 187ce9b54e1a..2b9423a173bb 100644 --- a/drivers/net/ethernet/intel/ice/ice_ptp_hw.c +++ b/drivers/net/ethernet/intel/ice/ice_ptp_hw.c @@ -274,6 +274,9 @@ void ice_ptp_src_cmd(struct ice_hw *hw, enum ice_ptp_tmr_cmd cmd) */ static void ice_ptp_exec_tmr_cmd(struct ice_hw *hw) { + struct ice_pf *pf = container_of(hw, struct ice_pf, hw); + + guard(spinlock)(&pf->adapter->ptp_gltsyn_time_lock); wr32(hw, GLTSYN_CMD_SYNC, SYNC_EXEC_CMD); ice_flush(hw); }