On Tue, Jun 10, 2025 at 01:36:38PM +0100, Daniel P. Berrangé wrote: > This series is an extension of Stefan's proposal: > > https://lists.nongnu.org/archive/html/qemu-devel/2025-06/msg00736.html > > It used '-Wframe-larger-than=4096' to identify all code locations > with more than 4k on the stack. Any locations in the I/O paths > were chosen to avoid automatic zero-init, to eliminate the performance > overhead of the automatic initialization. > > Note, although all the changed locations are I/O paths, this does not > imply that the changes make a measurement performance difference in > every case. > > This is because many of the emulated devices are likely limited by the > emulation impl, rather than any implicit memory zero'ing overhead of > stack data. > > None the less the memory zero'ing is still a redundant CPU burn in > all these cases, so I felt it worth setting the general precedent > that any data over 4k on a stack in a device I/O path should be > skipping zero-init. > > I did reasonable review in each case to identify that the data was > indeed initialized explicitly later in the method. > > Daniel P. Berrangé (29): > block: skip automatic zero-init of large array in ioq_submit > chardev/char-fd: skip automatic zero-init of large array > chardev/char-pty: skip automatic zero-init of large array > chardev/char-socket: skip automatic zero-init of large array > hw/audio/ac97: skip automatic zero-init of large arrays > hw/audio/cs4231a: skip automatic zero-init of large arrays > hw/audio/es1370: skip automatic zero-init of large array > hw/audio/gus: skip automatic zero-init of large array > hw/audio/gus: skip automatic zero-init of large array > hw/audio/sb16: skip automatic zero-init of large array > hw/audio/via-ac97: skip automatic zero-init of large array > hw/char/sclpconsole-lm: skip automatic zero-init of large array > hw/dma/xlnx_csu_dma: skip automatic zero-init of large array > hw/display/vmware_vga: skip automatic zero-init of large struct > hw/hyperv/syndbg: skip automatic zero-init of large array > hw/misc/aspeed_hace: skip automatic zero-init of large array > hw/net/rtl8139: skip automatic zero-init of large array > hw/net/tulip: skip automatic zero-init of large array > hw/net/virtio-net: skip automatic zero-init of large arrays > hw/net/xgamc: skip automatic zero-init of large array > hw/nvme/ctrl: skip automatic zero-init of large arrays > hw/ppc/pnv_occ: skip automatic zero-init of large struct > hw/ppc/spapr_tpm_proxy: skip automatic zero-init of large arrays > hw/usb/hcd-ohci: skip automatic zero-init of large array > hw/scsi/lsi53c895a: skip automatic zero-init of large array > hw/scsi/megasas: skip automatic zero-init of large arrays > hw/ufs/lu: skip automatic zero-init of large array > net/socket: skip automatic zero-init of large array > net/stream: skip automatic zero-init of large array > > Stefan Hajnoczi (2): > include/qemu/compiler: add QEMU_UNINITIALIZED attribute macro > hw/virtio/virtio: avoid cost of -ftrivial-auto-var-init in hot path > > block/linux-aio.c | 2 +- > chardev/char-fd.c | 2 +- > chardev/char-pty.c | 2 +- > chardev/char-socket.c | 2 +- > hw/audio/ac97.c | 4 ++-- > hw/audio/cs4231a.c | 4 ++-- > hw/audio/es1370.c | 2 +- > hw/audio/gus.c | 2 +- > hw/audio/marvell_88w8618.c | 2 +- > hw/audio/sb16.c | 2 +- > hw/audio/via-ac97.c | 2 +- > hw/char/sclpconsole-lm.c | 2 +- > hw/display/vmware_vga.c | 2 +- > hw/dma/xlnx_csu_dma.c | 2 +- > hw/hyperv/syndbg.c | 2 +- > hw/misc/aspeed_hace.c | 2 +- > hw/net/rtl8139.c | 2 +- > hw/net/tulip.c | 2 +- > hw/net/virtio-net.c | 6 +++--- > hw/net/xgmac.c | 2 +- > hw/nvme/ctrl.c | 6 +++--- > hw/ppc/pnv_occ.c | 2 +- > hw/ppc/spapr_tpm_proxy.c | 4 ++-- > hw/scsi/lsi53c895a.c | 2 +- > hw/scsi/megasas.c | 7 ++----- > hw/ufs/lu.c | 2 +- > hw/usb/hcd-ohci.c | 2 +- > hw/virtio/virtio.c | 8 ++++---- > include/qemu/compiler.h | 20 ++++++++++++++++++++ > net/socket.c | 2 +- > net/stream.c | 2 +- > 31 files changed, 61 insertions(+), 44 deletions(-) > > -- > 2.49.0 >
I will merge this series but want to give others a chance to review it first: Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
signature.asc
Description: PGP signature
