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 A74913AFAFE; Thu, 21 May 2026 11:43:48 +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=1779363833; cv=none; b=SlwGXe4R2zaD9CXVE7MgOhqySrdzeGhNXQ6H0rSbhdA8ikmvYSNSPe8D2TlcK+LHdHKN1Am7etdDCF7xesRKJ5I349iEzzRMQVU6rSJgP5Y4cdOlir3xwfidPsYQLIklDyrepml10Z0Nje0gjCeiufIvGuY4sztv9MAt0xPzOjo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779363833; c=relaxed/simple; bh=8gL+/BCazvMPnuYezqYq+fJwLn/fyLIJ1c4Q2FLUg7c=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=p+Ky9YTGd10KRAISM2sdm9HyNqm49brWHlRkoc76B21Luie+mdJA++7NTsYZMlBwJ2n+D9LcQiCR9S4eWGccFuTIrfy+kaYbQbWWtHxPARJUOuhUVf0JjU72O1Jf9jM3MC30elpRi8m546OlsS5mSnTzfirot8hLN+bctX3uaec= 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=HwBZJ1ud; 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="HwBZJ1ud" 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=9AMrOTNtZq75+jI/9CasCzJzwyJMfPiulP5Q4vSnukc=; b=HwBZJ1uddaqKjsj8sWu918CcUg h1XT9c9VfD+EF4W1uQwf7xFsml7fr37CdVyJFB/U4HcEXbO69y8D4Ye1xTZA7e5vuVAZR9p0xIKQM MI6Dx2ej2ODgUo+ox29cjRGGwoND2LMUsP6OENc3gK2fQlgcNl98eenePRwoVZUSIYh4cfC3y6JdJ ouqQyiSoaN7ck4zy7EMvfVV22PF6+qsA+URkD8xbVZkSKYb2NCTMu+bLIRwP1R9V5+JHNLiQS8Ax2 v0Mv4BRbq+7prTNS1Xd2kbqpRc/hDElVOOo4vZdt1RyZNen3HvB6LS/WVUuzXtI54cwwAB9OwHf/E LZUVhx/A==; 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 1wQ1oS-00000008Re4-1RZN; Thu, 21 May 2026 11:43:40 +0000 Message-ID: Subject: Re: [PATCH net-next v8 3/3] gve: implement PTP gettimex64 From: David Woodhouse To: Harshitha Ramamurthy , netdev@vger.kernel.org, Arthur Kiyanovski , tglx Cc: joshwash@google.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, richardcochran@gmail.com, jstultz@google.com, tglx@kernel.org, sboyd@kernel.org, willemb@google.com, nktgrg@google.com, jfraker@google.com, ziweixiao@google.com, maolson@google.com, jordanrhee@google.com, thostet@google.com, alok.a.tiwari@oracle.com, pkaligineedi@google.com, horms@kernel.org, jacob.e.keller@intel.com, yyd@google.com, jefrogers@google.com, linux-kernel@vger.kernel.org, Naman Gulati Date: Thu, 21 May 2026 12:43:38 +0100 In-Reply-To: <20260514225842.110706-4-hramamurthy@google.com> References: <20260514225842.110706-1-hramamurthy@google.com> <20260514225842.110706-4-hramamurthy@google.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-jVj3QwCCtynofXxEzSm6" User-Agent: Evolution 3.52.3-0ubuntu1.1 Precedence: bulk X-Mailing-List: netdev@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 --=-jVj3QwCCtynofXxEzSm6 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2026-05-14 at 22:58 +0000, Harshitha Ramamurthy wrote: >=20 > +static bool > +gve_can_use_system_ts_from_device(enum clocksource_ids system_clock_sour= ce, > + =C2=A0 clockid_t clockid) > +{ > + if (clockid !=3D CLOCK_REALTIME && clockid !=3D CLOCK_MONOTONIC_RAW) > + return false; > + > + /* If the system clock source matches the system clock > + * returned by the AdminQ command, we can use the system > + * timestamps returned by the device, otherwise we have to > + * fall back to sampling system time from the host which > + * is less accurate. > + */ > + if (IS_ENABLED(CONFIG_X86)) > + return system_clock_source =3D=3D CSID_X86_TSC; > + else if (IS_ENABLED(CONFIG_ARM64)) > + return system_clock_source =3D=3D CSID_ARM_ARCH_COUNTER; > + > + return false; Strictly, you could manage to convert to CSID_X86_KVM_CLK here too. The x86 kvm_arch_ptp_get_crosststamp() for ptp_kvm does so unconditionally. For ptp_vmclock we support both; we do the conversion only if the cs_id in the snapshot *is* the KVM clock, which seemed a bit more reasonable. And here you add a third variant which *only* copes with CSID_X86_TSC, to complete the set of possibilities :) With PTM and the various virt enlightenments, there are an increasing number of "PTP" clocks which literally *just* tell us a cycle count at the moment of the corresponding reading, and we don't need the ABA sandwich of local clock readings around it any more. I've got another one waiting in the wings which will literally just latch the counter value when a PPS signal comes in, too. It might be good to harmonise the way we convert to KVM clock if we're going to support that (although I'll accept an argument that any guest which chooses to use the KVM clock doesn't *deserve* to have accurate timekeeping). I'd also like consensus on exposing it to userspace. I think Thomas is going to suggest that we should always convert to MONOTONIC_RAW, but what I asked Arthur to do in=20 https://lore.kernel.org/all/20260515164033.6403-1-akiyano@amazon.com/ exposes the raw counter values instead. =46rom the dedicating hosting point of view, we *only* care about the counter, and absolutely DGAF about the host's timekeeping. Migrating KVM guests requires getting the guest TSC right (in terms of scaling factors and offset from the host TSC), and feeding accurate time to guests is done in terms of the guest TSC to realtime relationship. So our ideal state is that we discipline the TSC against real time in userspace, and enabling those PHC drivers to *give* us the raw cycle counts that they actually measured seemed best. Could we do that all on MONOTONIC_RAW, if Thomas insists? Maybe... although I like the model of disciplining one *specific* counter, and then telling the kernel about *that* counter. If the kernel for some reason has randomly switched to the HPET then the kernel is free to ignore what we're telling it about the TSC. --=-jVj3QwCCtynofXxEzSm6 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 GfZI+LGqSv0YtNa54T9D1AWJy08ZKkWvfGGIXN9UFAPMJ6OLLH/UUEgFa+7KlrEvMUupDFGnnR06 aDJAwtycb8yXtILj+TvfhLFhafxroXrflspavejQkEiHjNjtHnwbZ+o43g0/yxjwnarGI3kgcak7 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