Messages in this thread | | | Date | Wed, 15 Apr 2015 11:16:26 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/2] More precise timestamps for nested writes |
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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.
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