From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1008449A3D7 for ; Thu, 17 Sep 2026 23:03:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.69 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789686226; cv=none; b=icFkAmnUINxrqejshrQF91qiCmXks9mlHwwGZi61d1vbulSsLAk33sEkhq8E1Ez4K5tH103aS7Nd2fhLK3R1Z0FksdvSfqI3GfyL3E09FhTHt7kFSgc+OP4C1WdEXDbRhpvBqaXEz2IfE9ugzW/wtwk9p8pt7q4guZr87hT2ck0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789686226; c=relaxed/simple; bh=fX8Mv2j3jfcMNfxZ/Vvl78fSymNk3CAWNNUODUyuZUQ=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=b62Pin4eAg2yjJfahnvneXTW5y2cxaa4eVOB5qSIRtyr/EA86WghqQzkS2jgR7L5LaEQyfLNfZnbfFOfBYRRjANlqwSRj9R5xNg5ZjXZqnTMYInCNr8QR1IoqqFV76DRKtyfcshZvjHlu1QFl1C5b3Wq0DDFY4S7s2NC5QETa50= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--mclapinski.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=m2bxTF44; arc=none smtp.client-ip=209.85.128.69 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--mclapinski.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="m2bxTF44" Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-49cd55ee2f7so1111605e9.0 for ; Thu, 17 Sep 2026 16:03:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1789686212; x=1790291012; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:mime-version:date:from :to:cc:subject:date:message-id:reply-to:content-type; bh=oYAViEKIR6jmAp5mlWeLAMEKyuMg7x9lqO4x+CGM4FE=; b=m2bxTF44XTcKTpY3xqttoDLnQN4QjQHAEimEgc7Xu1QCNtCVZ7+4itg/IbrUaQHQoE gERpju5e6FjGobgSjq0jrR1froxe5iLWYu4KYGw9a82BowA+6m02Hm0iVp8qjHqJlf8o gL8puHyceBbzWE7VhHAnmvSg6c3DKTnTXpM8QIEd93sEWZevxYfmeGR3ICPEEUkJOnbW CuGPO2rAmL0SFPsfhYKn0h/PJMMZnuZDDbzQVsklDpAVDb17Ja4HPGbUKmakNkWHCnKu ff7IygsqHzcnn+SgOEaOFLmZE3gkcPtTWUlOlYqeHvutXbh7d2882WGS6rt2+gyzNg6C nCeQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1789686212; x=1790291012; h=content-type:cc:to:from:subject:message-id:mime-version:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=oYAViEKIR6jmAp5mlWeLAMEKyuMg7x9lqO4x+CGM4FE=; b=QoRxY/rzm3qowzxRvsiTiMYf4PPvmOmqTWNDE8ka1X5AU1UB7qftAmlsFUaRF0PltS xgcHyPqSy1IFvUy0wwssk1hxbQvtJQWrqTOtamFu7jIyZuNSHyVkyZ8wFxtVt198iTRR dx0IVMTRvMyDTokN2t9lbUjNEMlVJ6loXih8Ytmg06/ahi7YoR3rKDAnqdqGtjQ1pHI7 QT6rxxQ6b6OJ/rOmytRcTOzEKMA+/zf+BgNPnLm/HRsJCdpwt4C8yySsqrBWXa8BExjQ 01d1kwmkbJdo6oj4ZuteRoa3jQMD/wIh5vpXfXFeOr4FRqlqqftfFHGRFU7dw0iRT3jm NTow== X-Forwarded-Encrypted: i=1; AKwUvBzg5lov/38injqbqlqdBJv6jHAWIGID6mkSWtI+gnJ4jBBDgaQYcg+ZhmXYNJ0RNKWBky3+ByX44u38XlU=@vger.kernel.org X-Gm-Message-State: AFuF++kUFOr7jGIHdAzwV5HjdcdhvJo0XX4W3lQsLZE7h9kA/VWDTlEz gM5GGuVJ1Na4vonVrMKTLrFm5NARSgk2IrBRERTcH5DfCbcdiE7Ph1t2yyPDdoMIVQvHNW91YYG Kz1rDAFEAyWtEis/NiU21Yw== X-Received: from wmbds16.prod.google.com ([2002:a05:600c:6290:b0:49e:78cc:d2b]) (user=mclapinski job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:4695:b0:49c:d019:70c5 with SMTP id 5b1f17b1804b1-49fc55ac96emr5942785e9.0.1789686212281; Thu, 17 Sep 2026 16:03:32 -0700 (PDT) Date: Fri, 18 Sep 2026 01:03:23 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Message-ID: <20260917230323.3701743-1-mclapinski@google.com> Subject: [PATCH] PCI/DOE: Poll briefly for a response before sleeping From: Michal Clapinski To: Bjorn Helgaas , linux-pci@vger.kernel.org Cc: Lukas Wunner , Jonathan Cameron , Ira Weiny , Dan Williams , linux-kernel@vger.kernel.org, Michal Clapinski Content-Type: text/plain; charset="UTF-8" doe_statemachine_work() waits for a response by sleeping PCI_DOE_POLL_INTERVAL (PCI_DOE_TIMEOUT / 128) between status reads, which is 7 ms at HZ=1000 and 4 ms at HZ=250. Exchanges are served from the device's local mailbox logic and typically complete within tens of microseconds, so nearly all of that sleep is wasted. Every DOE-capable endpoint pays it once per supported feature during enumeration. Poll with usleep_range(20, 50) for the first ~2 ms before falling back to the jiffies-based wait. On an Intel Emerald Rapids system, time spent in pci_device_add() for a DOE-capable endpoint drops from 41.8 ms to 14.0 ms. Signed-off-by: Michal Clapinski --- drivers/pci/doe.c | 28 +++++++++++++++++++++++----- 1 file changed, 23 insertions(+), 5 deletions(-) diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c index ac95b1d2d999..6dc85133a88e 100644 --- a/drivers/pci/doe.c +++ b/drivers/pci/doe.c @@ -27,6 +27,9 @@ /* Timeout of 1 second from 6.30.2 Operation, PCI Spec r6.0 */ #define PCI_DOE_TIMEOUT HZ #define PCI_DOE_POLL_INTERVAL (PCI_DOE_TIMEOUT / 128) +#define PCI_DOE_POLL_FAST_MIN_US 20 +#define PCI_DOE_POLL_FAST_MAX_US 50 +#define PCI_DOE_POLL_FAST_TRIES 40 #define PCI_DOE_FLAG_CANCEL 0 #define PCI_DOE_FLAG_DEAD 1 @@ -486,7 +489,7 @@ static void doe_statemachine_work(struct work_struct *work) int offset = doe_mb->cap_offset; unsigned long timeout_jiffies; u32 val; - int rc; + int rc, tries = 0; if (test_bit(PCI_DOE_FLAG_DEAD, &doe_mb->flags)) { signal_task_complete(task, -EIO); @@ -524,10 +527,25 @@ static void doe_statemachine_work(struct work_struct *work) signal_task_abort(task, -EIO); return; } - rc = pci_doe_wait(doe_mb, PCI_DOE_POLL_INTERVAL); - if (rc) { - signal_task_abort(task, rc); - return; + /* + * Exchanges are served from the device's local mailbox + * logic and usually complete in tens of microseconds, far + * below the jiffies granularity of PCI_DOE_POLL_INTERVAL. + * Poll for up to ~2 ms before falling back to it. + */ + if (tries++ < PCI_DOE_POLL_FAST_TRIES) { + if (test_bit(PCI_DOE_FLAG_CANCEL, &doe_mb->flags)) { + signal_task_abort(task, -EIO); + return; + } + usleep_range(PCI_DOE_POLL_FAST_MIN_US, + PCI_DOE_POLL_FAST_MAX_US); + } else { + rc = pci_doe_wait(doe_mb, PCI_DOE_POLL_INTERVAL); + if (rc) { + signal_task_abort(task, rc); + return; + } } goto retry_resp; } -- 2.55.0.1082.g2b9226bbc0-goog