From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 569233E3173 for ; Mon, 25 May 2026 08:42:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779698532; cv=none; b=dYPcCOmOjttztRe8DPIhTOenI/3J7ZnzapplOwk2WBKOFZzKtMAaCvHud3Tm95Tgp2GT5IfXdQqEUV+Ifo9aqHEw08EdmRARk59eW1ztK9ytju1Pnb0sxGYe6UXzFCWGCp/xz5tz46UrftnK0Koh0ODadsCMhzEZUF3BDojmAKE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779698532; c=relaxed/simple; bh=tWSuPWqgy7fLpXP+BuEF5+dk03fOU6RuVPmDI2QT6j0=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=V4oNs1evOkDcgUyacbZAHDupvt5Y46BSTlWKlpAXtylFf5lyjzqQje1omiHavlIIzosuBtaN+fo/8EgpuRJMySPoTV/wWCWYK99mHa1dbWJJXi5tJ/Z9TClPIQ+WtiDxgYT2kceusSDtkNAG3kOur+zodM6dDtYZCcHeo0rqVI8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=casper.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=FgiPf1xv; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=casper.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="FgiPf1xv" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=tWSuPWqgy7fLpXP+BuEF5+dk03fOU6RuVPmDI2QT6j0=; b=FgiPf1xveoYkX9uXZlrrmy3iZV 26lxZBtGq9fWlBJAZmNo0+x6cWofgvQ/U5HhevBDfFLF9h+lm32p5H3AKAbIRPVL270sUcJlz4vkg si2TBPICPP257Rh05bhpvc5O6K1uA1yN31YdXbk9m3DoCIabD766+nCV6Bg4oQYcrlayb2hpm/+8i cX/PInSor+gdxL1wzm1JpEb3PAj+R1HD/BaT7Ht+xO7IKI5SckyiL5K2s/4O52PKw0Z4qgrrToQtZ RvGb2n43BDX3hk0Vd1LD6Ai+HZlYaV3qgXvjJqdSA6s7UQvIuoQuHBDYRQE4LFivDGZkSa4/E+pK6 FvWsBghA==; Received: from 54-240-197-239.amazon.com ([54.240.197.239] helo=u09cd745991455d.ant.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wRQsk-0000000GR05-0NWx; Mon, 25 May 2026 08:41:54 +0000 Message-ID: <887b97fadd6ba15d9e4585983610b4e70a018ee3.camel@infradead.org> Subject: Re: [RFC PATCH v2 0/8] timekeeping: Fix draft tracking precision and add feed-forward discipline via vmclock From: David Woodhouse To: Arthur Kiyanovski , Thomas Gleixner Cc: Miroslav Lichvar , Richard Cochran , Wen Gu , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , John Stultz , Stephen Boyd , Anna-Maria Behnsen , Frederic Weisbecker , Shuah Khan , Peter Zijlstra , Thomas =?ISO-8859-1?Q?Wei=DFschuh?= , Arnd Bergmann , Julien Ridoux , Ryan Luu , linux-kernel@vger.kernel.org, Marcelo Tosatti Date: Mon, 25 May 2026 09:41:52 +0100 In-Reply-To: <177969636528.22488.1740278196841124440.b4-reply@b4> References: <20260517220326.4625-1-dwmw2@infradead.org> <0d32da75fa88c92ac0225ef23a9045afdf2ac9fe.camel@infradead.org> <87o6i8vcni.ffs@tglx> <6c7137748ccea288fdf55e7c2e24817ccc1673ef.camel@infradead.org> <874ijzvpl8.ffs@tglx> <00609fa255442648e11e2b5596a3b80a29edcfc8.camel@infradead.org> <87v7cftqey.ffs@tglx> <87se7ht25o.ffs@tglx> <177969636528.22488.1740278196841124440.b4-reply@b4> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-EzJtXGNL70113LuwT9i1" User-Agent: Evolution 3.52.3-0ubuntu1.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html --=-EzJtXGNL70113LuwT9i1 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2026-05-25 at 08:06 +0000, Arthur Kiyanovski wrote: > Hi Thomas, David, Thanks, Arthur. > Thanks for the layout proposal, Thomas. The unified structure with=20 > explicit valid flags is a much cleaner approach than bounds-based > validation. >=20 > I'm the author of the PHC timestamp attributes series [1] that this > applies to. Before I spin v4 based on this design, I want to confirm > three implementation details: >=20 > 1. Counter IDs: No stable UAPI clocksource numbering exists today=20 > (enum clocksource_ids is kernel-internal). I'll define stable constants > in include/uapi/linux/ptp_clock.h (e.g., PTP_CSID_X86_TSC, > PTP_CSID_ARM_ARCH) and map internal IDs in the chardev layer. I think you'd already done a mapping like this to PTP_COUNTER_xxx, hadn't you? Although at the time I thought you'd mapped it to the VIRTIO_RTC_COUNTER_xxx and VMCLOCK_COUNTER_xxx values and now I see they don't quite match up. If I understood Thomas correctly, I think he meant that you should make the kernel's actual CSID values into uapi (which would involve moving the clocksource_ids.h file to include/uapi/).=20 I think I did have a slight preference for keeping an explicit mapping, and exposing only those CSIDs that we *intend* to expose to userspace (maybe not CSID_X86_TSC_EARLY, or we might make that to PTP_COUNTER_X86_TSC). But only if the number space does actually match VMCLOCK and VIRTIO_RTC.=20 I'm also *entirely* prepared to concede if Thomas really does want to expose CSID values directly; that isn't a hill to die on. > 2. Array sizing: The timestamps array will be fixed at PTP_MAX_SAMPLES (2= 5) > in the ioctl struct, not a flexible array, to keep > copy_from_user/copy_to_user bounded. >=20 > 3. Ioctl numbers: Two separate ioctls (PTP_SYS_OFFSET_EXTENDED_ATTRS and > PTP_SYS_OFFSET_PRECISE_ATTRS) sharing the same payload struct, matching > existing PTP convention. >=20 > Arthur >=20 > [1] https://lore.kernel.org/netdev/20260515164033.6403-1-akiyano@amazon.c= om/ >=20 --=-EzJtXGNL70113LuwT9i1 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj jfhCFqxYyRiW8g3cNFAvltDbK5AzcOaR7yVzVGadr4YcCVxjKrEJOgi7WEOH8rUgCNB5cTD8N/Et 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