On Wed, May 28, 2014 at 12:56:25PM -0400, Steven Rostedt wrote: > My concern is passing in a large string and wasting a lot of the ring > buffer space. The max you can hold per event is just under a page size > (4k). And all these strings add up. If it happens to be 512bytes, then > you end up with one event per page. I just don't understand why you say wasting memory. I just pass a char * not a string array. And most of time these strings are partial full, about 1/5 ~ 1/4 spaces are used.
>
> Instead of making that a huge string, what about a dynamic array of
> special structures?
>
>
> struct __attribute__((__packed__)) cper_sec_mem_rec {
> short type;
> int data;
> };
>
>
> static struct cper_sec_mem_rec mem_location[CPER_REC_LEN];
>
> then have the:
>
> if (mem->validation_bits & CPER_MEM_VALID_NODE) {
> msg[n].type = CPER_MEM_VALID_NODE_TYPE;
> msg[n++].data = mem->node;
> }
> if (mem->validation_bits & CPER_MEM_VALID_CARD) {
> msg[n].type = CPER_MEM_VALID_CARD_TYPE;
> msg[n++].data = mem->card;
> }
> if (mem->validation_bits & CPER_MEM_VALID_MODULE) {
> [ and so on ]
>
This function is not only for perf but for dmesg. So key is how
to handle two strings: dimm_location and mem_location.
I read some __print_symbolic implementations like btrfs trace,
#define show_ref_type(type) \
__print_symbolic(type, \
{ BTRFS_TREE_BLOCK_REF_KEY, "TREE_BLOCK_REF" }, \
{ BTRFS_EXTENT_DATA_REF_KEY, "EXTENT_DATA_REF" }, \
{ BTRFS_EXTENT_REF_V0_KEY, "EXTENT_REF_V0" }, \
{ BTRFS_SHARED_BLOCK_REF_KEY, "SHARED_BLOCK_REF" }, \
{ BTRFS_SHARED_DATA_REF_KEY, "SHARED_DATA_REF" })
So for this case, maybe we need a macro like:
#define show_dimm_location(type) \
__print_symbolic(type, \
{ CPER_MEM_VALID_NODE, "node" }, \
{ CPER_MEM_VALID_CARD, "card" }, \
{ CPER_MEM_VALID_MODULE, "module" }, \
...
IMO, it is just another implementation method, maybe more graceful,
but I don't know how it can save space. Again, original functions
work both for trace and dmesg. If we add such interface, it looks
a little bit repeated.
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