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X-IronPort-AV: E=Sophos;i="6.12,165,1728950400"; d="scan'208";a="776831212" Subject: RE: [PATCH v4 net-next 3/3] net: ena: Add PHC documentation Thread-Topic: [PATCH v4 net-next 3/3] net: ena: Add PHC documentation Received: from pdx4-co-svc-p1-lb2-vlan2.amazon.com (HELO smtpout.prod.us-east-1.prod.farcaster.email.amazon.dev) ([10.25.36.210]) by smtp-border-fw-9106.sea19.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Nov 2024 08:45:55 +0000 Received: from EX19MTAEUC002.ant.amazon.com [10.0.17.79:22286] by smtpin.naws.eu-west-1.prod.farcaster.email.amazon.dev [10.0.31.126:2525] with esmtp (Farcaster) id 37568dfa-9180-4a36-addc-82166bcb1c1f; Tue, 19 Nov 2024 08:45:53 +0000 (UTC) X-Farcaster-Flow-ID: 37568dfa-9180-4a36-addc-82166bcb1c1f Received: from EX19D010EUA004.ant.amazon.com (10.252.50.94) by EX19MTAEUC002.ant.amazon.com (10.252.51.181) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1258.34; Tue, 19 Nov 2024 08:45:53 +0000 Received: from EX19D005EUA002.ant.amazon.com (10.252.50.11) by EX19D010EUA004.ant.amazon.com (10.252.50.94) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1258.34; Tue, 19 Nov 2024 08:45:52 +0000 Received: from EX19D005EUA002.ant.amazon.com ([fe80::6aa4:b4a3:92f6:8e9]) by EX19D005EUA002.ant.amazon.com ([fe80::6aa4:b4a3:92f6:8e9%3]) with mapi id 15.02.1258.035; Tue, 19 Nov 2024 08:45:52 +0000 From: "Arinzon, David" To: Richard Cochran CC: David Miller , Jakub Kicinski , "netdev@vger.kernel.org" , Eric Dumazet , Paolo Abeni , "Woodhouse, David" , "Machulsky, Zorik" , "Matushevsky, Alexander" , "Bshara, Saeed" , "Wilson, Matt" , "Liguori, Anthony" , "Bshara, Nafea" , "Schmeilin, Evgeny" , "Belgazal, Netanel" , "Saidi, Ali" , "Herrenschmidt, Benjamin" , "Kiyanovski, Arthur" , "Dagan, Noam" , "Bernstein, Amit" , "Agroskin, Shay" , "Abboud, Osama" , "Ostrovsky, Evgeny" , "Tabachnik, Ofir" , "Machnikowski, Maciek" , Rahul Rameshbabu , Gal Pressman Thread-Index: AQHbNnwBYT2f8QoaH0qt+HbH+6LQELK6ugMAgAAB9wCAA5OIgA== Date: Tue, 19 Nov 2024 08:45:52 +0000 Message-ID: References: <20241114095930.200-1-darinzon@amazon.com> <20241114095930.200-4-darinzon@amazon.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 > On Sat, Nov 16, 2024 at 05:53:26PM -0800, Richard Cochran wrote: > > On Thu, Nov 14, 2024 at 11:59:30AM +0200, David Arinzon wrote: > > > > > +**phc_skp** Number of skipped get time attempts (during bloc= k > period). > > > +**phc_err** Number of failed get time attempts (entering int= o > block state). > > > > Just curious... I understand that the HW can't support a very high > > rate of gettime calls and that the driver will throttle them. > > > > But why did you feel the need to document the throttling behavior in > > such a overt way? Are there user space programs out there calling > > gettime excessively? >=20 > Answering my own question (maybe) >=20 > I see that your PHC only supports gettime(), and so I guess you must have > some atypical system setup in mind. >=20 > I didn't see any comments in the cover letter or in the patch about why t= he > PHC isn't adjustable or how offering gettime() only is useful? >=20 > Thanks, > Richard Hi Richard =09 Thank you for the queries. Our device limits the number of requests per client (VM) through throttling= . To avoid reaching our device throttling limit and ensure a fail-fast mechan= ism, the driver preemptively applies throttling. In addition, AWS cannot be adjusted or controlled by the OS/User to correct= any time deviations, instead, AWS manages the synchronization and accuracy of the clock internal= ly and provides a pre-disciplined clock that already adheres to Coordinated Universal Time (U= TC) standards. An upcoming patch, which is a continuation of https://lore.kernel.org/netde= v/4c2e99b4-b19e-41f5-a048-3bcc8c33a51c@lunn.ch/T/#m58cf9b05b34046b3952ae8bf= 4cc7d7f2c8b011d7, will introduce the error bound in ENA PHC, providing internal AWS accuracy = error measurements (in nanoseconds). Thanks, David