From nobody Mon Dec 1 22:03:45 2025 Received: from mail-pf1-f178.google.com (mail-pf1-f178.google.com [209.85.210.178]) (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 88290305E18 for ; Thu, 27 Nov 2025 19:43:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.178 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764272631; cv=none; b=N5CDb5hgC2tGA3iP+jrGTacNrL8LD9Wrl4TiwJSaCaH45vNO/CHESIK0kpw7P0RWbj1BI/BJrPjb10foI36bZEQWhtNFS6IXclz+4txGLsufRo71PWU4ufZU5utfNejId/f9JEIK0nBdOKNibGrT5kQyNRSr73VYVX4MEEkDXFY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764272631; c=relaxed/simple; bh=3QfrgidDXpfOyi97s2Qp8RLPHq0Fb501qY3wocX0jBc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CCDavoPb9Rwh5wBmMtXB09t/D4Wd4nfBtdYNFpBzBVjo7P4tqWb1uc4JmQutAPs3gAcTilQlcuMQkX6ACvDDpYJcLRlcj0tXW1a7wj4nuVoHsNUxaCvSHJYqvXqilnhM4phNQcJGZadDaKP3wCYqH1NREwJbaIphZrMIcnF0QWc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=chrisdown.name; spf=pass smtp.mailfrom=chrisdown.name; dkim=pass (1024-bit key) header.d=chrisdown.name header.i=@chrisdown.name header.b=pmohnUX/; arc=none smtp.client-ip=209.85.210.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=chrisdown.name Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=chrisdown.name Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=chrisdown.name header.i=@chrisdown.name header.b="pmohnUX/" Received: by mail-pf1-f178.google.com with SMTP id d2e1a72fcca58-7b89c1ce9easo1339291b3a.2 for ; Thu, 27 Nov 2025 11:43:46 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chrisdown.name; s=google; t=1764272625; x=1764877425; darn=vger.kernel.org; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=U2OhD2n8KTXhVixVHl0Vqn4ZBngMvrAZ6Kx7Y2aWb60=; b=pmohnUX/+6fEKjxczQHuPpDNAM/6WkO3RC3lc0+Et9hQjF2pwn9HiLiCRIS7QeWfSl VTX/aqjdhiXbhHLLOYWT+noBFPx38LsqqHrch6lZYbYOs/0oWXzlpBx/wEmmcdBBtE8q 1TMBz49qh0+ShgfTXT8sDB2/x5D/A3nwpmmWc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1764272625; x=1764877425; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=U2OhD2n8KTXhVixVHl0Vqn4ZBngMvrAZ6Kx7Y2aWb60=; b=Dge0Bp08uMVofisnSux6BysEOOHl45oLRvQRCQYsRRSoO6EAnmpMCz9IFZdLE4Wt4w vnpE13JsecgF5Sz7KGajy8XjWepwTRinGgO252gefiXdAYWem0KfOYkVKC8jdJt9Hrn/ j57R9Nr9Rck3VJ8aEp2OjXdhi3r9x7q7E7sUu87abbCa1U/P0BwOArwfzu+55kL3tIwL WbpO45lJWcsTlxYTlT4w8E4yiADm5+5mRLi2rPQfkRbIBs4v5+NJR7ezyL0hvGF5Szhq TEC+l+Siy/yPcf9cCCaI7waDbDUH6qEqcwCNBPqFfI5hbtC9U05/YF9eXx9+PVsoDs6s J1fg== X-Gm-Message-State: AOJu0YySakLOyTa13CQss61sE1L2oDujB7/8LCxkmYRCztqpbs6w8bs2 0GuRMP2HjBsKtXibcMCWxkMHiCRghkcTpcHvO+y32PNXUpCyPd1NPDHukx1PONOzju4= X-Gm-Gg: ASbGncsiRYqCewBryrHelG3byenYGCisqVCsg0bqoRu60nkyEch6LCXDbrBeamaEAEf EMRo0v7u641jJ6tT27ZHcKvoaHU4g7FfTwLGyB3fIf1YKB2SPKsLvvM6QgVCq5z6ICSmrb5u9vP iZyBbfVESip6r32Z5Ckj/R+ao2LISsbWMKxRCc5XqcO0F6+YD3rfg5FN+EiubcQQDnIVr5xDKhQ /1rOhiMPhX1r5Q6CJSj8FCCe/tavmJHjDGYyGSbP7FTTg6kIQDUp3D1AO8ss729c3uY2QlYiz5N MQuolU0KmimunPh8rkaMnRPdHLDyg3l2gj3ZuKc5HTqEEywy9tkrR9djjdteuLw15FCVpbh/+K+ y8946I8FrPrQH/mgKFlQN4jY824UOO/hswL474C+M9GYuIZyY15OUCt4ZvDA6dFibnVxyWggSLB xwJCkLZgkN X-Google-Smtp-Source: AGHT+IEcM0k7rWgEAwh97Jp0tYWXpssfqNqv1gwmrU+OYIjYCPqlUxiFYUoR5I8jKERWTCk0uu3p4w== X-Received: by 2002:a05:6a20:7d9e:b0:35d:5d40:6d79 with SMTP id adf61e73a8af0-36150e2be82mr25765948637.12.1764272625036; Thu, 27 Nov 2025 11:43:45 -0800 (PST) Received: from localhost ([116.86.198.140]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7d14b870a4dsm2743115b3a.0.2025.11.27.11.43.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Nov 2025 11:43:44 -0800 (PST) Date: Fri, 28 Nov 2025 03:43:42 +0800 From: Chris Down To: Petr Mladek Cc: linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Sergey Senozhatsky , Steven Rostedt , John Ogness , Geert Uytterhoeven , Tony Lindgren , kernel-team@fb.com Subject: [PATCH v8 09/21] printk: Optimise printk_delay() to avoid walking consoles under SRCU Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.2.15 (2b349c5e) (2025-10-02) Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" As part of the per-console loglevel implementation, printk_delay() introduces a call to suppress_message_printing_everywhere() within printk_delay(). This check acquires the console SRCU lock and iterates through all registered consoles to determine if the message implies a delay based on per-console loglevels. Since printk_delay() is called in the hotpath of vprintk_emit(), this introduces measurable overhead (locking and pointer chasing) for every printk message, even on systems where no delay is configured. Optimise this by short-circuiting the function. If neither a boot delay nor a runtime printk_delay_msec is configured, return immediately. This avoids the expensive console list iteration in the common case where delays are disabled. Signed-off-by: Chris Down --- kernel/printk/printk.c | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 0d7f3dac8177..13e17d892ec9 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2233,20 +2233,31 @@ int printk_delay_msec __read_mostly; =20 static inline void printk_delay(int level) { + bool boot_delay_active =3D false; + int m; + +#ifdef CONFIG_BOOT_PRINTK_DELAY + boot_delay_active =3D boot_delay && system_state < SYSTEM_RUNNING; +#endif + + if (!boot_delay_active && !READ_ONCE(printk_delay_msec)) + return; + /* If the message is forced (e.g. panic), we must delay */ if (!is_printk_force_console() && suppress_message_printing_everywhere(level)) return; =20 - boot_delay_msec(); + if (boot_delay_active) + boot_delay_msec(); =20 - if (unlikely(printk_delay_msec)) { - int m =3D printk_delay_msec; + m =3D READ_ONCE(printk_delay_msec); + if (!m) + return; =20 - while (m--) { - mdelay(1); - touch_nmi_watchdog(); - } + while (m--) { + mdelay(1); + touch_nmi_watchdog(); } } =20 --=20 2.51.2