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Mon, 26 Feb 2024 15:11:56 +0000 (UTC) Received: from toolbox.redhat.com (unknown [10.45.226.57]) by smtp.corp.redhat.com (Postfix) with ESMTP id BE5EB492BC6; Mon, 26 Feb 2024 15:11:54 +0000 (UTC) From: Michal Schmidt To: intel-wired-lan@lists.osuosl.org Date: Mon, 26 Feb 2024 16:11:24 +0100 Message-ID: <20240226151125.45391-3-mschmidt@redhat.com> In-Reply-To: <20240226151125.45391-1-mschmidt@redhat.com> References: <20240226151125.45391-1-mschmidt@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.9 X-Mailman-Original-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1708960322; 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=G/FILp3GfaUy8dt5HQEFRSG4sYMmu9jGA+QnSeAHKRE=; b=TACQ8sJyKHbfSG9QEus7+mZ/TP5BMysv0jDsC/7xYxGqty5XnG+kxtDVPt0OHTLHeMlUlJ 6iwjAuc/VOuZZoTXErTCcI4evPEUD7YQRQlgYVx+LI6Zdyx2zT/84H+gBeH7L9K1swU6HL O0xR9mFfn7yFziswfxMs8zfpeDjWyAw= X-Mailman-Original-Authentication-Results: smtp1.osuosl.org; dmarc=pass (p=none dis=none) header.from=redhat.com X-Mailman-Original-Authentication-Results: smtp1.osuosl.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=TACQ8sJy Subject: [Intel-wired-lan] [PATCH net-next 2/3] ice: avoid the PTP hardware semaphore in gettimex64 path X-BeenThere: intel-wired-lan@osuosl.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel Wired Ethernet Linux Kernel Driver Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: netdev@vger.kernel.org, Richard Cochran , Jesse Brandeburg , Arkadiusz Kubalewski , Karol Kolacinski , Jacob Keller Errors-To: intel-wired-lan-bounces@osuosl.org Sender: "Intel-wired-lan" 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 It consists of: - kernel threads reading the time in a busy loop and looking at the deltas between consecutive values, reporting new maxima. in the consecutive values; - 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 deb063401238..4b9f5d29811c 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" @@ -38,6 +39,7 @@ struct ice_adapter *ice_adapter_get(const struct pci_dev *pdev) if (!a) return NULL; + spin_lock_init(&a->ptp_gltsyn_time_lock); refcount_set(&a->refcount, 1); if (xa_is_err(xa_store(&ice_adapters, index, a, GFP_KERNEL))) { 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..b6c7246245c6 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_irqsave)(&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..a47dbbfadb74 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_irqsave)(&pf->adapter->ptp_gltsyn_time_lock); wr32(hw, GLTSYN_CMD_SYNC, SYNC_EXEC_CMD); ice_flush(hw); } -- 2.43.2