Quoting Ian McDonald:
| On 4/6/07, Gerrit Renker <gerrit@xxxxxxxxxxxxxx> wrote:
| > [CCID 3]: New RX History Step 2 - Initialisation and cleanup
| > +int tfrc_rx_hist_init(struct tfrc_rx_hist *h)
| > +{
| > + int i;
| > +
| > + for (i = 0; i <= NDUPACK; i++) {
| > + h->ring[i] = kmem_cache_alloc(tfrcxh->dccprxh_slab, GFP_ATOMIC);
| > + if (h->ring[i] == NULL)
| > + return 1;
| > + }
| > + spin_lock_init(&h->lock);
| > + h->loss_count = 0;
| > + h->loss_start = 0;
| > + return 0;
| > +}
| > +
| > +EXPORT_SYMBOL_GPL(tfrc_rx_hist_init);
|
| Given that you are allocating a fixed size amount of memory which is
| known at compile time I think that allocating one block per entry is
| the wrong approach and you lose half the value of having it in a ring
| buffer as you still have to dereference. This uses more memory to
| store each of the pointers and there is a good chance that they may
| not be contiguous in memory and thus your cache memory gets more
| dirty.
These are good points. Are you suggesting to kmalloc the entire array instead?
The main point which convinced me to use a slab cache was that the slab cache is
now global for the entire tfrc_lib module, i.e. when there are e.g. 10 CCID3
connections, they will all allocate from the same slab.
With regard to your second point, I quote from
http://www.erg.abdn.ac.uk/users/gerrit/dccp/docs/ccid3_packet_reception/loss_detection/loss_detection_algorithm_notes.txt
-------------------------------------------------------------------------------
1. 'ring' is an array of pointers rather than a contiguous area in
memory. The reason is that, when having to swap adjacent entries
to sort the history, it is easier to swap pointers than to copy
(heavy-weight) history-entry data structs.
-------------------------------------------------------------------------------
Given that pointer references are needed, is using kmalloc for each of the 4 entries
a better way than using the slab cache?
| I also share Eddies comment about the size of this.
Oops - then it means that you are also confusing RX history with LI database.
The LI database starts at patch #16 (12a) and ends at patch #24. This is the
receiver history structure, used for loss detection and RTT sampling. The LI
database has sufficient = 9 entries.
| NB I'm not saying that this shouldn't go in. I'm just saying this is
| not the most efficient.
If you can suggest any improvements, I'd be most happy to take them on board.
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