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

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Date:   Tue, 16 Aug 2022 12:41:28 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     ira.weiny@...el.com
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org
Subject: Re: [RFC PATCH 1/9] cxl/mem: Implement Get Event Records command

On Tue, 16 Aug 2022 12:39:58 -0400
Steven Rostedt <rostedt@...dmis.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