linux-kernel - Re: [PATCH v5 4/9] cxl/events: Remove passing a UUID to known event traces

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Date: Tue, 9 Jan 2024 15:38:28 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>, Ira Weiny
	<ira.weiny@...el.com>
CC: Dan Williams <dan.j.williams@...el.com>, Smita Koralahalli
	<Smita.KoralahalliChannabasappa@....com>, Shiju Jose <shiju.jose@...wei.com>,
	Yazen Ghannam <yazen.ghannam@....com>, Davidlohr Bueso <dave@...olabs.net>,
	Dave Jiang <dave.jiang@...el.com>, Alison Schofield
	<alison.schofield@...el.com>, Vishal Verma <vishal.l.verma@...el.com>, "Ard
 Biesheuvel" <ardb@...nel.org>, <linux-efi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>
Subject: Re: [PATCH v5 4/9] cxl/events: Remove passing a UUID to known event
 traces

Jonathan Cameron wrote:
> On Wed, 20 Dec 2023 16:17:31 -0800
> Ira Weiny <ira.weiny@...el.com> wrote:
> 
> > The UUID data is redundant in the known event trace types.  The addition
> > of static defines allows the trace macros to create the UUID data inside
> > the trace thus removing unnecessary code.
> > 
> > Have well known trace events use static data to set the uuid field based
> > on the event type.
> > 
> > Suggested-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> > Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> > 
> 
> >  	TP_STRUCT__entry(
> >  		CXL_EVT_TP_entry
> > @@ -422,7 +424,8 @@ TRACE_EVENT(cxl_dram,
> >  	),
> >  
> >  	TP_fast_assign(
> > -		CXL_EVT_TP_fast_assign(cxlmd, log, uuid, rec->hdr);
> > +		CXL_EVT_TP_fast_assign(cxlmd, log, rec->hdr);
> > +		memcpy(&__entry->hdr_uuid, &CXL_EVENT_DRAM_UUID, sizeof(uuid_t));
> 
> Hmm. Why not
> 
> 		__entry->hdr_uuid = CXL_EVENT_DRAM_UUID;
> ?
> 
> Compiler should be able to squish the stuff in the define down to data as as the
> UUID generation logic is pretty simple.
> 
> I've not emulated the cper records for these yet, so not tested that works beyond
> compiling.

We can follow on with this conversion later as I see other usage of uuid
copying in trace events (bcache for instance). Although I probably would
not replace it with straight assignment and instead use the uuid_copy()
helper. Otherwise, why do {uuid,guid}_copy() helpers exist?