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[80.230.24.117]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f63ed1911sm4114351f8f.22.2026.07.17.06.55.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Jul 2026 06:55:37 -0700 (PDT) Date: Fri, 17 Jul 2026 09:55:34 -0400 From: "Michael S. Tsirkin" To: Peter Maydell Cc: Gavin Shan , qemu-arm@nongnu.org, qemu-devel@nongnu.org, peterx@redhat.com, alex@shazbot.org, richard.henderson@linaro.org, berrange@redhat.com, philmd@oss.qualcomm.com, philmd@mailo.com, david@kernel.org, clg@redhat.com, pbonzini@redhat.com, phrdina@redhat.com, jugraham@redhat.com, liugang24219@sangfor.com.cn, dinghui@sangfor.com.cn, shan.gavin@gmail.com Subject: Re: [PATCH v3 1/2] system/memory: Use qemu_ram_{copy, move}() in ram device region accessors Message-ID: <20260717095407-mutt-send-email-mst@kernel.org> References: <20260625091334-mutt-send-email-mst@kernel.org> <20260625101817-mutt-send-email-mst@kernel.org> <20260625123119-mutt-send-email-mst@kernel.org> <5faf04b9-d596-4a1d-9fe3-5e9ad5f0a99a@redhat.com> <73f79841-8cc7-4ca6-8f6b-fb97b53a6fe8@redhat.com> <20260717091756-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Ur8LXOsxDsanuHYEDKWpa_GO5QbK0KNlTvKHvONZ_70_1784296539 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: permerror client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.01, SPF_HELO_PASS=-0.001, T_SPF_PERMERROR=0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org On Fri, Jul 17, 2026 at 02:49:53PM +0100, Peter Maydell wrote: > On Fri, 17 Jul 2026 at 14:24, Michael S. Tsirkin wrote: > > > > On Thu, Jul 09, 2026 at 07:52:12PM +1000, Gavin Shan wrote: > > > Hi Michael and Peter, > > > > > > > Could you help to confirm if the conclusion is to have unified qemu_ram_{copy, move}() > > > for all architectures? In qemu_ram_{copy, move}(), the fixed sized accesses like > > > 1/2/4/8 bytes are handled by __builtin_{memcpy, memmove}() and fall back to > > > memcpy/memmove() for other sized accesses. It's basically what was proposed by > > > Michael :-) > > > > No. __builtin_ and memcpy/memmove are same on modern linuxes. > > > > I'd say as a 1st step, on x86 hosts we can do a fixed size > > memmove for 1/2/4/8, on other hosts > > *aligned* 1/2/4/8 bytes can do > > __atomic_store ... __ATOMIC_RELAXED > > and the rest can hobble along on memmove > > and hope for the best. > > I don't think we should be doing something that's x86-host specific, > as I've mentioned previously. > > -- PMM Shrug. Of course we already have arch specific code in asm. But we can make the unaligned 1/2/4/8 for x86 host a separate optimization on top. They are unlikely to be common. -- MST