On Mon, Apr 13, 2015 at 09:38:01PM -0500, Suresh E. Warrier wrote: > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index c9b3005..0a2d862 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -482,6 +482,7 @@ struct ring_buffer_per_cpu { > unsigned long read_bytes; > u64 write_stamp; > u64 read_stamp; > + u64 last_stamp; > /* ring buffer pages to update, > 0 to add, < 0 to remove */ > int nr_pages_to_update; > struct list_head new_pages; /* new pages to add */
So what is wrong with something like: u64 rb_get_delta(struct ring_buffer_per_cpu *cpu_buffer) { u64 last, now; for (;;) { last = cpu_buffer->last_stamp; now = cpu_buffer->buffer->clock(); if (cmpxchg_local(&cpu_buffer->last_stamp, last, now) == last) break; cpu_relax(); } return now - last; } Of course, LL/SC on power stinks, but on most archs this is actually fairly fast. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/