From nobody Thu Aug 24 19:29:06 2023 X-Original-To: dev-commits-src-all@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 4RWtSH5wBFz4rVW8 for ; Thu, 24 Aug 2023 19:29:19 +0000 (UTC) (envelope-from wlosh@bsdimp.com) Received: from mail-lf1-x12b.google.com (mail-lf1-x12b.google.com [IPv6:2a00:1450:4864:20::12b]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "smtp.gmail.com", Issuer "GTS CA 1D4" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4RWtSG6gy1z3CTM for ; Thu, 24 Aug 2023 19:29:18 +0000 (UTC) (envelope-from wlosh@bsdimp.com) Authentication-Results: mx1.freebsd.org; none Received: by mail-lf1-x12b.google.com with SMTP id 2adb3069b0e04-5007f3d3235so225197e87.2 for ; Thu, 24 Aug 2023 12:29:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bsdimp-com.20221208.gappssmtp.com; s=20221208; t=1692905357; x=1693510157; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=xAtRoBPI6o1brlauqNlyBhavbXTFoKd+7654kWRXewI=; b=bQWwFrsflR5zbSXiFXVMQ1FHZD4Sgs0qy1i+edvCAOMcscM3XoM5GcbwvQr/PA51vO wjfN62ChXE5e4P6MFsF7oshPIcVuweQWVgxrB1kIJT9ChqwhFt1JTQ9pwgE4OvsBsqAW mEbzp49bY7cNMpi0UpWb9w5SbWOPyi3cUFQmm8wAU7NFOmyCCeHG3BljVn9GWM1Nmzkb Na8eJt8VKdb4KbYDY1uBDs5qO8bEx+Fv9u5/b50K/+FjEry763G7KXR2Ds28K3Ra27mw zSvoiSMc7Os7k+PVsb6tuUhrCYfHFqrZufrkpjCKqx8fM81vFLlI4tJyOIOg0CvKDm0c zsmA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1692905357; x=1693510157; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=xAtRoBPI6o1brlauqNlyBhavbXTFoKd+7654kWRXewI=; b=QCXccf8lXeJhOiW0RCgi1FhYSgSPQmqlziNf7mpAXCu17K8kFuzkjhbwQnynFAa9DE 1m0Kjb6HRhgbN2ZLoaz+dj8+Rcels9N/Wd49L8rebGYlNP6uBSEbd7OOalf3F5Mt0yj8 Cj1vZJmVqWdTZrAqMB6eOhZ5UnWciCCsKP4UG7K8aMkBg1ZYFrprjmALELJeKh30un4U vtgWDoJuIpPojB1ii09cUYq/Bl1BWZdqAbzBuGSwfSKcluUeZdk99Ewby6clLVGL89zB HCD5Xo62U9aVCo0qS6rWQJzoU3Teg/55tk8kKGM98dhqSbg2k06dElWD8VmYLegzLLae Ufpw== X-Gm-Message-State: AOJu0YyMWJNK2mSIq/kk0YEQaGuFMmN6ILtrFDQdxCCYZJSRLP96ZfcO xCfUMUWjaPFFU3kkppJWz3ELCeecVzjwwkaVBtfTTUrUMm9xGgpw X-Google-Smtp-Source: AGHT+IE+v9dsKWldHjZze7sylatTXcwRSYPFo/lOvpegnUdB+/l44dlhb/Ai9NRcr62GCjpbtXTFg6goQNVgr9gxNDw= X-Received: by 2002:ac2:562f:0:b0:4f8:4512:c844 with SMTP id b15-20020ac2562f000000b004f84512c844mr11215957lff.48.1692905357014; Thu, 24 Aug 2023 12:29:17 -0700 (PDT) List-Id: Commit messages for all branches of the src repository List-Archive: https://lists.freebsd.org/archives/dev-commits-src-all List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-dev-commits-src-all@freebsd.org X-BeenThere: dev-commits-src-all@freebsd.org MIME-Version: 1.0 References: <202308230007.37N07cOK082906@gitrepo.freebsd.org> <748B7A01-5011-44EE-BB04-282AE96F9B5B@freebsd.org> <0F3EA94D-6696-471C-ABF6-840B5E92967F@freebsd.org> <747e34d5-8191-5fb9-deb4-c94d7f1693e0@FreeBSD.org> In-Reply-To: <747e34d5-8191-5fb9-deb4-c94d7f1693e0@FreeBSD.org> From: Warner Losh Date: Thu, 24 Aug 2023 13:29:06 -0600 Message-ID: Subject: Re: git: 4a69fc16a583 - main - Add membarrier(2) To: John Baldwin Cc: Jessica Clarke , Konstantin Belousov , "src-committers@freebsd.org" , "dev-commits-src-all@freebsd.org" , "dev-commits-src-main@freebsd.org" Content-Type: multipart/alternative; boundary="0000000000007190d10603b03e8c" X-Rspamd-Queue-Id: 4RWtSG6gy1z3CTM X-Spamd-Bar: ---- X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[]; ASN(0.00)[asn:15169, ipnet:2a00:1450::/32, country:US] --0000000000007190d10603b03e8c Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, Aug 24, 2023 at 10:19=E2=80=AFAM John Baldwin wro= te: > On 8/23/23 6:01 AM, Warner Losh wrote: > > On Tue, Aug 22, 2023 at 11:37=E2=80=AFPM Jessica Clarke > wrote: > > > >> > >>> The addition does not change any existing code path in the kernel. > >> > >> No, but it commits us to a new syscall being stable just days before 1= 4 > >> branches and has its ABI frozen. > >> > > > > I'd planned on committing timerfd later today. I didn't consider it an > ABI > > breakage, since it was just additive. It's one of the things that can b= e > > MFC'd (we don't prohibit new system calls). > > (Not taking a side on the merits of the current membarrier(2) > implementation) > > I think Jess's point here is not that a new syscall is not a valid ABI > breakage, but more that once you add a new syscall that makes it into a > release, now the ABI of that syscall is frozen and can't be changed. Tha= t > said, syscall numbers are relatively "cheap", so if we had to renumber > membarrier(2) because its ABI was found to be a problem that could be don= e, > albeit at the cost of keeping the old one around under COMPAT_FREEBSD. > OK. I jumped to the wrong conclusion... Good points all around. Warner --0000000000007190d10603b03e8c Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


=
On Thu, Aug 24, 2023 at 10:19=E2=80= =AFAM John Baldwin <jhb@freebsd.org> wrote:
On= 8/23/23 6:01 AM, Warner Losh wrote:
> On Tue, Aug 22, 2023 at 11:37=E2=80=AFPM Jessica Clarke <jrtc27@freebsd.org> wr= ote:
>
>>
>>> The addition does not change any existing code path in the ker= nel.
>>
>> No, but it commits us to a new syscall being stable just days befo= re 14
>> branches and has its ABI frozen.
>>
>
> I'd planned on committing timerfd later today. I didn't consid= er it an ABI
> breakage, since it was just additive. It's one of the things that = can be
> MFC'd (we don't prohibit new system calls).

(Not taking a side on the merits of the current membarrier(2) implementatio= n)

I think Jess's point here is not that a new syscall is not a valid ABI<= br> breakage, but more that once you add a new syscall that makes it into a
release, now the ABI of that syscall is frozen and can't be changed.=C2= =A0 That
said, syscall numbers are relatively "cheap", so if we had to ren= umber
membarrier(2) because its ABI was found to be a problem that could be done,=
albeit at the cost of keeping the old one around under COMPAT_FREEBSD<n&= gt;.

OK. I jumped to the wrong conclusi= on...=C2=A0 Good points all around.


Warner
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