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Tsirkin" , Peter Maydell , qemu-block@nongnu.org, Stefan Hajnoczi , Kevin Wolf , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Subject: [PATCH 28/31] hw/scsi/megasas: skip automatic zero-init of large arrays Date: Tue, 10 Jun 2025 13:37:06 +0100 Message-ID: <20250610123709.835102-29-berrange@redhat.com> In-Reply-To: <20250610123709.835102-1-berrange@redhat.com> References: <20250610123709.835102-1-berrange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@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-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1749559822623116600 The 'megasas_dcmd_pd_get_list' and 'megasas_dcmd_get_properties' methods have 4k structs used for copying data from the device. Skip the automatic zero-init of this array to eliminate the performance overhead in the I/O hot path. The 'info' structs are manually initialized with memset(). The compiler ought to be intelligent enough to turn the memset() into a static initialization operation, and thus not duplicate the automatic zero-init. Replacing memset() with '{}' makes it unambiguous that the arrays are statically initialized. Signed-off-by: Daniel P. Berrang=C3=A9 --- hw/scsi/megasas.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c index 55cd188bd5..844643d916 100644 --- a/hw/scsi/megasas.c +++ b/hw/scsi/megasas.c @@ -981,13 +981,11 @@ static int megasas_event_wait(MegasasState *s, Megasa= sCmd *cmd) =20 static int megasas_dcmd_pd_get_list(MegasasState *s, MegasasCmd *cmd) { - struct mfi_pd_list info; - size_t dcmd_size =3D sizeof(info); + struct mfi_pd_list info =3D {}; BusChild *kid; uint32_t offset, dcmd_limit, num_pd_disks =3D 0, max_pd_disks; dma_addr_t residual; =20 - memset(&info, 0, dcmd_size); offset =3D 8; dcmd_limit =3D offset + sizeof(struct mfi_pd_address); if (cmd->iov_size < dcmd_limit) { @@ -1429,11 +1427,10 @@ static int megasas_dcmd_cfg_read(MegasasState *s, M= egasasCmd *cmd) =20 static int megasas_dcmd_get_properties(MegasasState *s, MegasasCmd *cmd) { - struct mfi_ctrl_props info; + struct mfi_ctrl_props info =3D {}; size_t dcmd_size =3D sizeof(info); dma_addr_t residual; =20 - memset(&info, 0x0, dcmd_size); if (cmd->iov_size < dcmd_size) { trace_megasas_dcmd_invalid_xfer_len(cmd->index, cmd->iov_size, dcmd_size); --=20 2.49.0