From: Peter Zijlstra <peterz@infradead.org>
To: "Suresh E. Warrier" <warrier@linux.vnet.ibm.com>
Cc: lklml <linux-kernel@vger.kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Ingo Molnar <mingo@redhat.com>, Paul Mackerras <paulus@samba.org>
Subject: Re: [PATCH 2/2] More precise timestamps for nested writes
Date: Wed, 15 Apr 2015 11:16:26 +0200 [thread overview]
Message-ID: <20150415091626.GF17717@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <552C7D89.2080802@linux.vnet.ibm.com>
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.
next prev parent reply other threads:[~2015-04-15 9:16 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1428459449-10664-1-git-send-email-warrier@linux.vnet.ibm.com>
2015-04-14 2:29 ` [PATCH 0/2] ring-buffer: More precise timestamps for nested writes Suresh E. Warrier
2015-04-14 2:31 ` [PATCH 1/2] ring-buffer: Introduce precise nested timestamp sysfs attribute Suresh E. Warrier
2015-04-14 2:38 ` [PATCH 2/2] More precise timestamps for nested writes Suresh E. Warrier
2015-04-14 17:13 ` Peter Zijlstra
2015-04-15 0:33 ` Suresh E. Warrier
2015-04-15 8:45 ` Peter Zijlstra
2015-04-15 9:16 ` Peter Zijlstra [this message]
2015-04-15 16:53 ` Suresh E. Warrier
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