From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) (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 813CD5111B9; Wed, 9 Sep 2026 12:47:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.12 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788958083; cv=none; b=hqsuXP5g9waByv59loAyoSTg9CNPiufP3aA0+t2enMy7A9KwxmR9V9HkYKhXRi853ei2DX0ZL+kFHVTMHoruAOjafrh1yrLpAN3E3dQm0WgTi/u9W1sfqPMr8DgqgTJlQhzBhtApo/sW479WSmH/5yXIe48/7LHAauSWt58p57E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788958083; c=relaxed/simple; bh=UH6njIIyQR9OD67VxOrA7ozK5cAuBO8Er8TuNdULDmc=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=ec2/gKAaWTT8ZSzgi89GZVcZVdSI2nXoVvD13AnodoP6g+Hc7nByfqtcyLpVn4d6W639mMyLcS76LUmzHqJlXSxyAmOfppdF4JbTyySfGon8BpDPukp117JBmdU1CdqNwXf+Buf/g/rIvDDyD4p3RKI6qihmFtx0GXtw7RjfGgU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; dkim=pass (1024-bit key) header.d=goodmis.org header.i=@goodmis.org header.b=ADDLMYnF; arc=none smtp.client-ip=216.40.44.12 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=goodmis.org header.i=@goodmis.org header.b="ADDLMYnF" Received: from omf02.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 4C8ADA0202; Wed, 9 Sep 2026 12:47:55 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf02.hostedemail.com (Postfix) with ESMTPA id 2ED5B80015; Wed, 9 Sep 2026 12:47:50 +0000 (UTC) Date: Wed, 9 Sep 2026 08:49:06 -0400 From: Steven Rostedt To: Ran Hongyun Cc: , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [QUESTION] Are these issues PREEMPT_RT-specific? Message-ID: <20260909084906.75ebe0ea@gandalf.local.home> In-Reply-To: <20260909030506.344667-1-ranhongyun1@huawei.com> References: <63d5cd58e9b85acccdaaac9aed4a8c550cc7b868.camel@siemens.com> <20260909030506.344667-1-ranhongyun1@huawei.com> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 2ED5B80015 X-Stat-Signature: o3fwibtfheyjf6uxcieed6spah8gf4o6 X-Rspamd-Server: rspamout03 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX19Xhy7OK4OBMc93k3sLXpaXbNrFBmTU+H4= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=goodmis.org; h=date:from:to:cc:subject:message-id:in-reply-to:references:mime-version:content-type:content-transfer-encoding; s=dkim1; bh=2JZIG0evn7FRLH7buEDQNvcDz4SWp2iw0ronrwwEllg=; b=ADDLMYnF3uDGdfsjFF0AU4mcXm38KNdi8JQJqfv2s53fOhf4+RXiDVgvjxqa2qfF+eWgYXqLtvVi2r6E08M1MGNT+fqqwDF52gB0YKtOpd7t4QfDjaEHj1AhZqNh9XZiz5cv79QyyIa6+fo1PJChOsle7nl88pcyxnhjlfRkMhU= X-HE-Tag: 1788958070-860100 X-HE-Meta: U2FsdGVkX197gq9AYxmfVVmX8SBppYiJWxnth8UqyGIuz6uN3lbwz0pQN7siOw3O4K0M7d4v3vNtgdpSjudf8Q3H833uzaqs1ZB9LiXp/7l6WMYMfifkrHrWiG3iE4YpahG4qYMB/z74IxWPawDwy+le3fYdPgQZIBe6+TktybcVJeTH3KS9TtSQJiWLN4Rf3I9iLhilR9Uhgnch0QOvP7kUktj5KHGRuGz+rEHhAL14UZZkhrroFB52+2Oo2d1S8Z/IMYhj1hfDgtrfuPTvugC5o0UhmQzs+HeDWnndpf6D8+/C80z7YhEhGTv8oy4mQQIn7yLB4nr8YGUvVuOZDrUBMKR44PXZ On Wed, 9 Sep 2026 11:05:05 +0800 Ran Hongyun wrote: > Florian, >=20 > Thank you for your reply. >=20 > Now I understand that the issues are particularly critical on PREEMPT_RT.= =20 > However, I=E2=80=99m still not entirely clear about the "performance or t= hroughput > drop" you mentioned for !RT systems. Since !RT kernels are > non-preemptible, unbounded priority inversion and stalls should not occur. That is incorrect. !RT kernels have been preemptible for decades. There are different levels: SERVER - non preemptible (but no distributions use that) VOLUNTARY - Has preemptible points in the kernel (might_sleep()) - most d= istros used this FULL - Preempts everywhere that doesn't turn off preemption RT - Turns spin locks into mutexes and preempts there too Regardless of that, unbound priority inversion can happen even in SERVER mode. All it takes is three tasks sharing a mutex. Only RT implements priority inheritance (for all locks but reader locks) in the kernel which would prevent unbounded priority inversion with normal locks. > Are there any other factors that could still cause such a performance or > throughput drop? >=20 > In other words, if I am running a !RT system, what benefit can I actually > expect from switching from rwlock to spinlock? Lack of priority inheritance is true for both RT and !RT in rwlocks. Hence that does affect both of them. -- Steve