From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <tdevries@suse.de>
Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29])
 by sourceware.org (Postfix) with ESMTPS id 1850B3858C53
 for <gdb-patches@sourceware.org>; Sun, 17 Jul 2022 13:15:37 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 1850B3858C53
Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74])
 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)
 key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512)
 (No client certificate requested)
 by smtp-out2.suse.de (Postfix) with ESMTPS id 4800B1FD3C;
 Sun, 17 Jul 2022 13:15:36 +0000 (UTC)
Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74])
 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)
 key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512)
 (No client certificate requested)
 by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 339C613A83;
 Sun, 17 Jul 2022 13:15:36 +0000 (UTC)
Received: from dovecot-director2.suse.de ([192.168.254.65])
 by imap2.suse-dmz.suse.de with ESMTPSA id mz1mC3gL1GKVSQAAMHmgww
 (envelope-from <tdevries@suse.de>); Sun, 17 Jul 2022 13:15:36 +0000
Message-ID: <4225064d-73d9-52bd-fc21-341e787af40b@suse.de>
Date: Sun, 17 Jul 2022 15:15:35 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.9.0
Subject: Re: [committed][gdb/symtab] Make per_cu->unit_type atomic
Content-Language: en-US
To: Tom Tromey <tom@tromey.com>,
 Tom de Vries via Gdb-patches <gdb-patches@sourceware.org>
References: <20220714061940.GA575@delia.home> <874jzht55r.fsf@tromey.com>
From: Tom de Vries <tdevries@suse.de>
In-Reply-To: <874jzht55r.fsf@tromey.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Spam-Status: No, score=-6.6 required=5.0 tests=BAYES_00, DKIM_SIGNED,
 DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, NICE_REPLY_A, SPF_HELO_NONE,
 SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
 server2.sourceware.org
X-BeenThere: gdb-patches@sourceware.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gdb-patches mailing list <gdb-patches.sourceware.org>
List-Unsubscribe: <https://sourceware.org/mailman/options/gdb-patches>,
 <mailto:gdb-patches-request@sourceware.org?subject=unsubscribe>
List-Archive: <https://sourceware.org/pipermail/gdb-patches/>
List-Post: <mailto:gdb-patches@sourceware.org>
List-Help: <mailto:gdb-patches-request@sourceware.org?subject=help>
List-Subscribe: <https://sourceware.org/mailman/listinfo/gdb-patches>,
 <mailto:gdb-patches-request@sourceware.org?subject=subscribe>
X-List-Received-Date: Sun, 17 Jul 2022 13:15:38 -0000

On 7/16/22 18:04, Tom Tromey wrote:
>>>>>> "Tom" == Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> writes:
> 
> Tom> -  packed<dwarf_unit_type, 1> m_unit_type = (dwarf_unit_type) 0;
> Tom> +  std::atomic<packed<dwarf_unit_type, 1>> m_unit_type {(dwarf_unit_type)0};
>   
> I was thinking about this patch this morning and I wonder if packed<> is
> even needed now that the member is atomic.

With packed:
...
   std::atomic<packed<dwarf_unit_type, 1>> m_unit_type {(dwarf_unit_type)0};
...
we have:
...
         /* size: 120, cachelines: 2, members: 22 */
...
and without:
...
   std::atomic<dwarf_unit_type> m_unit_type {(dwarf_unit_type)0};
...
we have:
...
         /* size: 128, cachelines: 2, members: 22 */
...

So it's necessary to keep the struct small.

Thanks,
- Tom