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 CC1CD17DE17; Tue, 25 Jun 2024 21:34:26 +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=1719351268; cv=none; b=l3KffkhG9C1bdSNPI1vmC45CchKEs9KaJVMx9xPzPsjjA5HPcxiSgd/CZfuoQ90tnWuF59WxqKFkkiURLosEzQXhHis2v62ksgCGNki25+yVOV8E7Wv02ibg0G6rRSCcy9T1Jh7GmeyeNLCSMiINO1Cq6thiHNIc69WtwJJHbCg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719351268; c=relaxed/simple; bh=HfaYGuuRwJRfrYo4iNSGZYDprWu7BbdzxDPdNxmmntI=; h=From:To:Cc:Subject:In-Reply-To:Date:Message-ID:MIME-Version: Content-Type; b=aPSnZk+pnVSXd7kL2y3W3e5gsifiUhX8aLxE7+DA/Z98W4UJzWjJby/WPCF5DbBwKtBY4eJ9SRrHo6yiXEgUcOdeHM0u6fK+NNlke3MvDFR5eeGM66aP1iVmw94iizkxhxkxEQkyDVJgMYpVRPmr1HjffqY1tRbBxkSWEcI342o= 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=xd7xbvHP; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=fG2hs6PZ; 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="xd7xbvHP"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="fG2hs6PZ" From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1719351265; 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; bh=cBD4zAiF08Tny5sO1Gl2HsuBxAKc5MasJfQRkmugnwI=; b=xd7xbvHPrn0WWfzg6B74Sg+5WddYaCIiEgHS+QlK6NmVrMF20WaHrkqdQfEMAYH8W0Lebe jomz94JOpYib8BIKcjNhQgcCBrkX+NSLbumPeu56wdF4zMiNMJ+lXwB9GfP/L3ZVFt923O gDVbv6trHv1Me6PNZWEJvST0AR+biixf/+ieWv0lKZWqvdhSxWCmauQynkfOgfCLuEg8MY bwApIHOJDPq3ZzOZf1v5D/aDLePpYqMAV1v5Fl0SCwxw8D9h1lnO3eIUfE5l+utbW5PKc/ KssfZ8E6EdpbwOiQ9H5qzUCFeD9UW6q7uvCfMGvAM8p6xqZRdVzgPo8LiBTqYw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1719351265; 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; bh=cBD4zAiF08Tny5sO1Gl2HsuBxAKc5MasJfQRkmugnwI=; b=fG2hs6PZ+vtjj+L3x1f4wBjXlrHsTMYW87osvADsyB7iust7q/iXbfYchPW6bVeSfgjt11 Kgiu2FLgNLLz/ADQ== To: David Woodhouse , Peter Hilber , linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-rtc@vger.kernel.org, "Ridoux, Julien" , virtio-dev@lists.linux.dev, "Luu, Ryan" Cc: "Christopher S. Hall" , Jason Wang , John Stultz , "Michael S. Tsirkin" , netdev@vger.kernel.org, Richard Cochran , Stephen Boyd , Xuan Zhuo , Marc Zyngier , Mark Rutland , Daniel Lezcano , Alessandro Zummo , Alexandre Belloni Subject: Re: [RFC PATCH v2] ptp: Add vDSO-style vmclock support In-Reply-To: <4a0a240dffc21dde4d69179288547b945142259f.camel@infradead.org> Date: Tue, 25 Jun 2024 23:34:24 +0200 Message-ID: <87jzic4sgv.ffs@tglx> Precedence: bulk X-Mailing-List: linux-rtc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Tue, Jun 25 2024 at 20:01, David Woodhouse wrote: > From: David Woodhouse > > The vmclock "device" provides a shared memory region with precision clock > information. By using shared memory, it is safe across Live Migration. > > Like the KVM PTP clock, this can convert TSC-based cross timestamps into > KVM clock values. Unlike the KVM PTP clock, it does so only when such is > actually helpful. > > The memory region of the device is also exposed to userspace so it can be > read or memory mapped by application which need reliable notification of > clock disruptions. There is effort underway to expose PTP clocks to user space via VDSO. Can we please not expose an ad hoc interface for that? As you might have heard the sad news, I'm not feeling up to the task to dig deeper into this right now. Give me a couple of days to look at this with working brain. Thanks, tglx