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hw/scsi/megasas: skip automatic zero-init of large arrays

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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. Berrangé <berrange@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Message-id: 20250610123709.835102-29-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Daniel P. Berrangé 2025-06-10 13:37:06 +01:00 • committed by Stefan Hajnoczi
parent 55243edf42
commit ca0559e235
1 changed files with 2 additions and 5 deletions
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7
hw/scsi/megasas.c
View file

@ -981,13 +981,11 @@ static int megasas_event_wait(MegasasState *s, MegasasCmd *cmd)
static int megasas_dcmd_pd_get_list(MegasasState *s, MegasasCmd *cmd)
{
struct mfi_pd_list info;
size_t dcmd_size = sizeof(info);
struct mfi_pd_list info = {};
BusChild *kid;
uint32_t offset, dcmd_limit, num_pd_disks = 0, max_pd_disks;
dma_addr_t residual;
memset(&info, 0, dcmd_size);
offset = 8;
dcmd_limit = offset + sizeof(struct mfi_pd_address);
if (cmd->iov_size < dcmd_limit) {
@ -1429,11 +1427,10 @@ static int megasas_dcmd_cfg_read(MegasasState *s, MegasasCmd *cmd)
static int megasas_dcmd_get_properties(MegasasState *s, MegasasCmd *cmd)
{
struct mfi_ctrl_props info;
struct mfi_ctrl_props info = {};
size_t dcmd_size = sizeof(info);
dma_addr_t residual;
memset(&info, 0x0, dcmd_size);
if (cmd->iov_size < dcmd_size) {
trace_megasas_dcmd_invalid_xfer_len(cmd->index, cmd->iov_size,
dcmd_size);