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[79.242.62.5]) by smtp.gmail.com with ESMTPSA id b24sm3559718wmj.43.2021.09.03.01.47.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 03 Sep 2021 01:47:35 -0700 (PDT) To: Peter Xu References: <20210902131432.23103-1-david@redhat.com> <20210902131432.23103-8-david@redhat.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v4 7/9] migration: Simplify alignment and alignment checks Message-ID: <8985fca4-e15c-95a7-2c45-74353a3a19fa@redhat.com> Date: Fri, 3 Sep 2021 10:47:34 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -53 X-Spam_score: -5.4 X-Spam_bar: ----- X-Spam_report: (-5.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.39, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-2.225, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eduardo Habkost , Juan Quintela , Pankaj Gupta , "Michael S. Tsirkin" , teawater , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , Alex Williamson , Marek Kedzierski , Paolo Bonzini , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Andrey Gruzdev , Wei Yang Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 03.09.21 00:32, Peter Xu wrote: > On Thu, Sep 02, 2021 at 03:14:30PM +0200, David Hildenbrand wrote: >> diff --git a/migration/migration.c b/migration/migration.c >> index bb909781b7..ae97c2c461 100644 >> --- a/migration/migration.c >> +++ b/migration/migration.c >> @@ -391,7 +391,7 @@ int migrate_send_rp_message_req_pages(MigrationIncomingState *mis, >> int migrate_send_rp_req_pages(MigrationIncomingState *mis, >> RAMBlock *rb, ram_addr_t start, uint64_t haddr) >> { >> - void *aligned = (void *)(uintptr_t)(haddr & (-qemu_ram_pagesize(rb))); >> + void *aligned = (void *)QEMU_ALIGN_DOWN(haddr, qemu_ram_pagesize(rb)); > > Is uintptr_t still needed? I thought it would generate a warning otherwise but > not sure. It doesn't in my setup, but maybe it will on 32bit archs ... I discussed this with Phil in https://lkml.kernel.org/r/2c8d80ad-f171-7d5f-3235-92f02fa174b3@redhat.com Maybe QEMU_ALIGN_PTR_DOWN((void *)haddr, qemu_ram_pagesize(rb))); Is really what we want. > > Also, maybe ROUND_DOWN() is better? QEMU_ALIGN_DOWN is the slow version for > arbitrary numbers. We do have exactly 2 direct users of ROUND_DOWN() in the tree (well, we do have some more for ROUND_UP) :) QEMU_ALIGN_DOWN vs. QEMU_ALIGN_DOWN is much easier to map and understand IMHO, and there is usually little need to optimize. I actually do wonder how much of a difference it actually makes on modern CPUs ... -- Thanks, David / dhildenb