From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <dev-bounces@dpdk.org>
Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124])
	by inbox.dpdk.org (Postfix) with ESMTP id 72FFB44098;
	Wed, 22 May 2024 17:37:45 +0200 (CEST)
Received: from mails.dpdk.org (localhost [127.0.0.1])
	by mails.dpdk.org (Postfix) with ESMTP id EC29D402C2;
	Wed, 22 May 2024 17:37:44 +0200 (CEST)
Received: from mail-pf1-f176.google.com (mail-pf1-f176.google.com
 [209.85.210.176])
 by mails.dpdk.org (Postfix) with ESMTP id F1BC7400D6
 for <dev@dpdk.org>; Wed, 22 May 2024 17:37:43 +0200 (CEST)
Received: by mail-pf1-f176.google.com with SMTP id
 d2e1a72fcca58-6f447976de7so2418067b3a.1
 for <dev@dpdk.org>; Wed, 22 May 2024 08:37:43 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
 d=networkplumber-org.20230601.gappssmtp.com; s=20230601; t=1716392263;
 x=1716997063; darn=dpdk.org; 
 h=content-transfer-encoding:mime-version:references:in-reply-to
 :message-id:subject:cc:to:from:date:from:to:cc:subject:date
 :message-id:reply-to;
 bh=OCsoByC9NfL7ZEf7FKgJF/1Tjsr7yQNB4pkw9bz2O/g=;
 b=wJDhi4DV8iQ9G5bOulMjnOct3P9G5g77am5W8/iJO7xMODpyUOnrxiGqHX+FeapD3k
 zTEKneLNA/wGCPXunM45+RHFJoKli+C/yJWKkBWfU+hL4I5Y5mc0Y87eDYfJb9+skcG5
 CKtfVgFPY7SThA7SdnZoZBXi7unM7oYT1S3fvwVLL4Cwsp+WRK9U10xcwd9gt9JyAUKu
 b0ceSM/F70Pv3uMkjUrTOlXOFlI/NKY+ZryhmZdQL93xEK3SyDx/2kC+j1a2mI5tHNID
 hUN+qFUxFWcqp3/Wwq9OBqy/WkyKn4eMapYAtk0SEu9TXr0Df9dK+6ms8J/lROfDd5e/
 5YmQ==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
 d=1e100.net; s=20230601; t=1716392263; x=1716997063;
 h=content-transfer-encoding:mime-version:references:in-reply-to
 :message-id:subject:cc:to:from:date:x-gm-message-state:from:to:cc
 :subject:date:message-id:reply-to;
 bh=OCsoByC9NfL7ZEf7FKgJF/1Tjsr7yQNB4pkw9bz2O/g=;
 b=gF0Kr1t3+vDPR6HVo8315/4JJeQ+5H8L06Cm9KPBLQ2/FapzZ3zPe8mWZptoPFeCvu
 PxxYTYn+vz+NsKASHtrBWpxMAcF3QBXM/nJ0O4TFpPk74+EVm9Jp1yodmS8WRxH3ck+R
 CyFdcP6b56+POp7MRSDb/7ebPF0IRalftCMQ9A/z9qxmrjpXNYOZZKN/SM5UHfOs9YwB
 naqwoVhoQxSH2yrFxWmsPpSXDqCoCVAkDbXMC+Q7KW7psaaAdUSwcd4bRSmjBaDGpbGO
 nwz8iw4YiZsheZLHte3n+7x7UPS07GABwf8vRem3fCOyF+xhDfxt904YwWQnUu72QfQh
 YY5Q==
X-Gm-Message-State: AOJu0Yz4rwC8xaokxB3NIeMaiRjqTBWbRwwcjLU5iQggg6sf7BFftMyg
 AEftgT0AAa9lhsVptLufXsqvQhvQR/13mihMh6tVy/lALeP2FaBAsJw7NcHrIxoWs7TVNrKOE7D
 CSRM=
X-Google-Smtp-Source: AGHT+IE4mQVIiuMSIEr0GJGJEWDtSzvHbMImrvTdevHVZBFi+NlddrKrhndk7yH3s+O27BRDl60ULQ==
X-Received: by 2002:a05:6a00:2311:b0:6ec:faff:ec1f with SMTP id
 d2e1a72fcca58-6f6d606a5a9mr2578771b3a.11.1716392263014; 
 Wed, 22 May 2024 08:37:43 -0700 (PDT)
Received: from hermes.local (204-195-96-226.wavecable.com. [204.195.96.226])
 by smtp.gmail.com with ESMTPSA id
 d2e1a72fcca58-6f66e4a24f4sm14067354b3a.0.2024.05.22.08.37.42
 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256);
 Wed, 22 May 2024 08:37:42 -0700 (PDT)
Date: Wed, 22 May 2024 08:37:41 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: Morten =?UTF-8?B?QnLDuHJ1cA==?= <mb@smartsharesystems.com>
Cc: <dev@dpdk.org>, "Tyler Retzlaff" <roretzla@linux.microsoft.com>
Subject: Re: [PATCH v9 1/8] eal: generic 64 bit counter
Message-ID: <20240522083741.64078d7e@hermes.local>
In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35E9F488@smartserver.smartshare.dk>
References: <20240510050507.14381-1-stephen@networkplumber.org>
 <20240521201801.126886-1-stephen@networkplumber.org>
 <20240521201801.126886-2-stephen@networkplumber.org>
 <98CBD80474FA8B44BF855DF32C47DC35E9F488@smartserver.smartshare.dk>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
X-BeenThere: dev@dpdk.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: DPDK patches and discussions <dev.dpdk.org>
List-Unsubscribe: <https://mails.dpdk.org/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://mails.dpdk.org/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <https://mails.dpdk.org/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
Errors-To: dev-bounces@dpdk.org

On Wed, 22 May 2024 10:31:39 +0200
Morten Br=C3=B8rup <mb@smartsharesystems.com> wrote:

> > +/* On 32 bit platform, need to use atomic to avoid load/store tearing =
*/
> > +typedef RTE_ATOMIC(uint64_t) rte_counter64_t; =20
>=20
> As shown by Godbolt experiments discussed in a previous thread [2], non-t=
earing 64 bit counters can be implemented without using atomic instructions=
 on all 32 bit architectures supported by DPDK. So we should use the counte=
r/offset design pattern for RTE_ARCH_32 too.
>=20
> [2]: https://inbox.dpdk.org/dev/98CBD80474FA8B44BF855DF32C47DC35E9F433@sm=
artserver.smartshare.dk/


This code built with -O3 and -m32 on godbolt shows split problem.

#include <stdint.h>

typedef uint64_t rte_counter64_t;

void
rte_counter64_add(rte_counter64_t *counter, uint32_t val)
{
	*counter +=3D val;
}
=E2=80=A6	*counter =3D val;
}

rte_counter64_add:
        push    ebx
        mov     eax, DWORD PTR [esp+8]
        xor     ebx, ebx
        mov     ecx, DWORD PTR [esp+12]
        add     DWORD PTR [eax], ecx
        adc     DWORD PTR [eax+4], ebx
        pop     ebx
        ret

rte_counter64_read:
        mov     eax, DWORD PTR [esp+4]
        mov     edx, DWORD PTR [eax+4]
        mov     eax, DWORD PTR [eax]
        ret
rte_counter64_set:
        movq    xmm0, QWORD PTR [esp+8]
        mov     eax, DWORD PTR [esp+4]
        movq    QWORD PTR [eax], xmm0
        ret