Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756655AbdIHRXg (ORCPT ); Fri, 8 Sep 2017 13:23:36 -0400 Received: from twosheds.infradead.org ([90.155.92.209]:34968 "EHLO twosheds.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752132AbdIHRXf (ORCPT ); Fri, 8 Sep 2017 13:23:35 -0400 Message-ID: <1504891402.32080.5.camel@infradead.org> Subject: Re: [PATCH v2 0/2] enable hires timer to timeout datagram socket From: David Woodhouse To: David Miller , eduval@amazon.com Cc: vallish@amazon.com, shuah@kernel.org, richardcochran@gmail.com, xiyou.wangcong@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, anchalag@amazon.com, dwmw@amazon.com In-Reply-To: <20170908.101657.2131282706895004921.davem@davemloft.net> References: <1503447027-44399-1-git-send-email-vallish@amazon.com> <20170822.213030.1848111782253505433.davem@davemloft.net> <20170908170409.GA10020@u40b0340c692b58f6553c.ant.amazon.com> <20170908.101657.2131282706895004921.davem@davemloft.net> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-yIlj8/oXgStC9J5aELTQ" Date: Fri, 08 Sep 2017 18:23:22 +0100 Mime-Version: 1.0 X-Mailer: Evolution 3.18.5.2-0ubuntu3.2 X-SRS-Rewrite: SMTP reverse-path rewritten from by twosheds.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8558 Lines: 136 --=-yIlj8/oXgStC9J5aELTQ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2017-09-08 at 10:16 -0700, David Miller wrote: > From: Eduardo Valentin > Date: Fri, 8 Sep 2017 10:04:09 -0700 >=20 > >=20 > > However, this is a clear, the system call, from the net subsystem, > > has changed in behavior across kernel versions. From application / > > userspace perspective, changing the system call without clear > > documentation or deprecation path, to me, looks like breaking > > userspace, isn't it? > > Where is the chapter and verse of the system call documentation that > guaranteed this level of timer granularity for you? >=20 > Or were you simply relying upon implementation dependent behavior? > I can't see anything which ever guarateed the granularity of timers > to the extent upon which you were relying. >=20 > And most importantly, letting the kernel have flexibility in this area > is absolutely essential for various forms of optimizations and power > savings. The rule we normally use, typically enforced very shoutily by Linus, is that *however* stupid userspace was to rely on something, if they *do* rely on it then we shouldn't change it. I don't know that anyone's ever tried saying "show me the chapter and verse of the documentation" to Linus when he's in full rant mode, as he tends to get in such discussions. You could try it, I suppose. I don't think 'HZ=3D=3D100' was documented per se either, was it? Perhaps we *could* change that, after all? :) (Not that I've actually looked at the patch or the userspace in question yet, mind you. Just commenting on the absurdity of the response.) --=-yIlj8/oXgStC9J5aELTQ Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCDzUw ggSvMIIDl6ADAgECAhEA4CPLFRKDU4mtYW56VGdrITANBgkqhkiG9w0BAQsFADBvMQswCQYDVQQG EwJTRTEUMBIGA1UEChMLQWRkVHJ1c3QgQUIxJjAkBgNVBAsTHUFkZFRydXN0IEV4dGVybmFsIFRU UCBOZXR3b3JrMSIwIAYDVQQDExlBZGRUcnVzdCBFeHRlcm5hbCBDQSBSb290MB4XDTE0MTIyMjAw MDAwMFoXDTIwMDUzMDEwNDgzOFowgZsxCzAJBgNVBAYTAkdCMRswGQYDVQQIExJHcmVhdGVyIE1h bmNoZXN0ZXIxEDAOBgNVBAcTB1NhbGZvcmQxGjAYBgNVBAoTEUNPTU9ETyBDQSBMaW1pdGVkMUEw PwYDVQQDEzhDT01PRE8gU0hBLTI1NiBDbGllbnQgQXV0aGVudGljYXRpb24gYW5kIFNlY3VyZSBF bWFpbCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAImxDdp6UxlOcFIdvFamBia3 uEngludRq/HwWhNJFaO0jBtgvHpRQqd5jKQi3xdhTpHVdiMKFNNKAn+2HQmAbqUEPdm6uxb+oYep LkNSQxZ8rzJQyKZPWukI2M+TJZx7iOgwZOak+FaA/SokFDMXmaxE5WmLo0YGS8Iz1OlAnwawsayT 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