On Fri, 18 May 2007 17:10:02 +0530
"pradeep singh" <2500.pradeep@xxxxxxxxx> wrote:
> Hi ,
>
> following code snippet is self evident in what it does -
>
> truct net_device *alloc_netdev(int sizeof_priv, const char *name,
> void (*setup)(struct net_device *))
> {
> void *p;
> struct net_device *dev;
> int alloc_size;
>
> /* ensure 32-byte alignment of both the device and private area */
> alloc_size = (sizeof(*dev) + NETDEV_ALIGN_CONST) & ~NETDEV_ALIGN_CONST;
> alloc_size += sizeof_priv + NETDEV_ALIGN_CONST;
>
> p = kzalloc(alloc_size, GFP_KERNEL);
> if (!p) {
> printk(KERN_ERR "alloc_dev: Unable to allocate device.\n");
> return NULL;
> }
> [snip]
>
> Is the comment correct?
yes it seems correct
> Why is it 'ensure 32 byte alignment', instead of 32 bit alignment?
Its 32 bytes, not bits.
#define NETDEV_ALIGN 32
#define NETDEV_ALIGN_CONST (NETDEV_ALIGN - 1)
>
> What am i missing here?
I dont know :)
This 32 bytes alignement maybe not up2date, because net_device contains several ____cacheline_aligned_in_smp
Would be nice to switch the alignement to max(L1_CACHE_SIZE, 32) nowadays, at least on SMP
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