Re: [RFC PATCH 1/9] cxl/mem: Implement Get Event Records command

From: Steven Rostedt <rostedt@goodmis.org>
To: ira.weiny@intel.com
Cc: Dan Williams <dan.j.williams@intel.com>,
	Alison Schofield <alison.schofield@intel.com>,
	Vishal Verma <vishal.l.verma@intel.com>,
	Ben Widawsky <bwidawsk@kernel.org>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org
Subject: Re: [RFC PATCH 1/9] cxl/mem: Implement Get Event Records command
Date: Tue, 16 Aug 2022 12:41:28 -0400	[thread overview]
Message-ID: <20220816124128.618948e9@gandalf.local.home> (raw)
In-Reply-To: <20220816123958.2b49674a@gandalf.local.home>

On Tue, 16 Aug 2022 12:39:58 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> > +		record_count = le16_to_cpu(payload.record_count);
> > +		if (record_count > 0)
> > +			trace_cxl_event(dev_name(cxlds->dev), type,
> > +					&payload.record);
> > +
> > +		if (payload.flags & CXL_GET_EVENT_FLAG_OVERFLOW)
> > +			trace_cxl_event_overflow(dev_name(cxlds->dev), type,
> > +						 &payload);  
> 
> If you want to avoid the compare operations when the tracepoints are not
> enabled, you can add:
> 
> 		if (trace_cxl_event_enabled()) {
> 			if (record_count > 0)
> 				trace_cxl_event(dev_name(cxlds->dev), type,
> 						&payload.record);
> 		}
> 
> 		if (trace_cxl_event_overflow_enabled()) {
> 			if (payload.flags & CXL_GET_EVENT_FLAG_OVERFLOW)
> 				trace_cxl_event_overflow(dev_name(cxlds->dev), type,
> 							 &payload);
> 		}
> 
> Those "<tracepoint>_enabled()" functions are static branches. Which means
> when not enabled it's a nop that skips this code, and when either is
> enabled, it turns into a jump to the contents of the if block.

Ignore this suggestion. I see in the second patch you add more logic to the
if condition. Only use this suggestion if the logic is only for when the
tracepoint is enabled.

-- Steve