From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 401D97CF25 for ; Thu, 8 Feb 2024 15:23:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707405841; cv=none; b=pJnJ8vVk7BxaHSSU9i8rIIsrD4Pp5wV5fXJbNP8cQyhQymcOnmHg7m8fa+TwCspk62zUi4PLkiWr0OyiTtnj4V6//a83Fln/9541hXiExzGtSuzuVUpS/7J119wLIX4tUtpm2Nwagp8VWuLFIr5IeNN9KzuYP+PKD4XMQBiqxaI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707405841; c=relaxed/simple; bh=TXFqJl+VejqNcQc19S9a0yo1TsUlfDoX2zcdznVhVOM=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=NtI4GMEXygbWsaCZApwV1vj4TyjKqKf/ZgXe3IwJfj6fWNTFt8sghC5tQTrF9DhuHCbDSupVRWnDKZDysgi85c/fXmBrVPJ/in0zQmgGw2DPJL/zw5GQDdYtYr1OvVbcaj+6WsfVpBxWi6zB5ghH62NmzwWNmSkcw0U2yVXTRRM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=ltOYCkeW; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=UX1fbATa; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="ltOYCkeW"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="UX1fbATa" From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1707405838; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=1FduTETIMSh9ur/MljH5h2gohj0pSlcSQSBY5yBtqTM=; b=ltOYCkeWx00OsUOMcZ7fKtADFlEpW7RCaaeg3pIN5BdzYvBMn5VfQftyf9c4wKCUznZ9uI rWgKMPHVJ+nZNL/LsxtZFkWJZkV2UncJYJbyC4YrGYcP2hyNqTRBN+qWh5swblac+rucIt GG6Lh25RPuMERxOL+dyYukQvV1L9jY0RDkVNYdkpP3dVpIeKoSUetPisJXuLdgXzyw6mGy xn1UQMPWv2HBUaIHTWOWl0a31Li5lRW4kCt1phq3dmsNa1/Z+DAYdmEUiaFBJyluz1lIjI Ttzy6Kw1jl1Tj77iYYuU14NVCFLDFuTYKYBi5OW725ncyLMAMNozJqKzym81TA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1707405838; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=1FduTETIMSh9ur/MljH5h2gohj0pSlcSQSBY5yBtqTM=; b=UX1fbATalMtYxRzrC/EaMHJvq0xjPwMgZGMOVsaJfoIZQaUpCBk0eFixUL0EOLkqbUh07E Zn3szRFUHu/swrDA== To: Marcelo Tosatti Cc: linux-kernel@vger.kernel.org, Daniel Bristot de Oliveira , Juri Lelli , Valentin Schneider , Frederic Weisbecker , Leonardo Bras , Peter Zijlstra Subject: Re: [patch 05/12] timekeeping_notify: use stop_machine_fail when appropriate In-Reply-To: References: <20240206184911.248214633@redhat.com> <20240206185709.955049547@redhat.com> <87h6ikmqqo.ffs@tglx> Date: Thu, 08 Feb 2024 16:23:58 +0100 Message-ID: <87zfwbkmi9.ffs@tglx> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Wed, Feb 07 2024 at 09:58, Marcelo Tosatti wrote: > On Wed, Feb 07, 2024 at 12:57:19PM +0100, Thomas Gleixner wrote: >> On Tue, Feb 06 2024 at 15:49, Marcelo Tosatti wrote: >> > Change timekeeping_notify to use stop_machine_fail when appropriate, >> > which will fail in case the target CPU is tagged as block interference >> > CPU. >> >> You completely fail to explain 'appropriate'. There is zero reason for >> this churn, really. > > The churn is so that we can return an error to > current_clocksource_store (sysfs handler for writes to > /sys/devices/system/clocksource/clocksource0/current_clocksource). What for? Why? Writing to that file requires root. Root can rightfully screw up a system and adding a debugfs based "prevention" mechanism is not making this any better because root can just clear the CPU mask there and move on. So what is the actual real world problem solved by these patches? All I've seen so far is handwaving about interference prevention and TBH I can't squint hard enough to believe that. Thanks, tglx