Hi David,
nice to see you getting started with it.
I'm not sure about the queue logic there.
1867 /* Caller must have exclusive producer access to the netchannel. */
1868 int netchannel_enqueue(struct netchannel *np, struct netchannel_buftrailer *bp)
1869 {
1870 unsigned long tail;
1871
1872 tail = np->netchan_tail;
1873 if (tail == np->netchan_head)
1874 return -ENOMEM;
This looks wrong, since empty and full are the same condition in your
case.
1891 struct netchannel_buftrailer *__netchannel_dequeue(struct netchannel *np)
1892 {
1893 unsigned long head = np->netchan_head;
1894 struct netchannel_buftrailer *bp = np->netchan_queue[head];
1895
1896 BUG_ON(np->netchan_tail == head);
See?
What about sth. like
struct netchannel {
/* This is only read/written by the writer (producer) */
unsigned long write_ptr;
struct netchannel_buftrailer *netchan_queue[NET_CHANNEL_ENTRIES];
/* This is modified by both */
atomic_t filled_entries; /* cache_line_align this? */
/* This is only read/written by the reader (consumer) */
unsigned long read_ptr;
}
This would prevent this bug from the beginning and let us still use the
full queue size.
If cacheline bouncing because of the shared filled_entries becomes an issue,
you are receiving or sending a lot.
Then you can enqueue and dequeue multiple and commit the counts later.
To be done with a atomic_read, atomic_add and atomic_sub on filled_entries.
Maybe even cheaper with local_t instead of atomic_t later on.
But I guess the cacheline bouncing will be a non-issue, since the whole
point of netchannels was to keep traffic as local to a cpu as possible, right?
Would you like to see a sample patch relative to your tree,
to show you what I mean?
Regards
Ingo Oeser
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