On Jun 10 13:37, Daniel P. Berrangé wrote:
> The 'nvme_map_sgl' method has a 256 element array 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 'segment' array will be fully initialized when reading data from
> the device.
>
> The 'nme_changed_nslist' method has a 4k byte array that is 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 array is statically initialized.
>
> Signed-off-by: Daniel P. Berrangé <berra...@redhat.com>
> ---
> hw/nvme/ctrl.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
> index fd935507bc..220002830d 100644
> --- a/hw/nvme/ctrl.c
> +++ b/hw/nvme/ctrl.c
> @@ -1057,7 +1057,8 @@ static uint16_t nvme_map_sgl(NvmeCtrl *n, NvmeSg *sg,
> NvmeSglDescriptor sgl,
> */
> #define SEG_CHUNK_SIZE 256
>
> - NvmeSglDescriptor segment[SEG_CHUNK_SIZE], *sgld, *last_sgld;
> + QEMU_UNINITIALIZED NvmeSglDescriptor segment[SEG_CHUNK_SIZE];
> + NvmeSglDescriptor *sgld, *last_sgld;
> uint64_t nsgld;
> uint32_t seg_len;
> uint16_t status;
> @@ -5128,7 +5129,7 @@ static uint16_t nvme_error_info(NvmeCtrl *n, uint8_t
> rae, uint32_t buf_len,
> static uint16_t nvme_changed_nslist(NvmeCtrl *n, uint8_t rae, uint32_t
> buf_len,
> uint64_t off, NvmeRequest *req)
> {
> - uint32_t nslist[1024];
> + uint32_t nslist[1024] = {};
> uint32_t trans_len;
> int i = 0;
> uint32_t nsid;
> @@ -5138,7 +5139,6 @@ static uint16_t nvme_changed_nslist(NvmeCtrl *n,
> uint8_t rae, uint32_t buf_len,
> return NVME_INVALID_FIELD | NVME_DNR;
> }
>
> - memset(nslist, 0x0, sizeof(nslist));
> trans_len = MIN(sizeof(nslist) - off, buf_len);
>
> while ((nsid = find_first_bit(n->changed_nsids, NVME_CHANGED_NSID_SIZE))
> !=
> --
> 2.49.0
>
> Reviewed-by: Klaus Jensen <k.jen...@samsung.com>
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