linux-kernel - Re: [PATCH V2 03/11] cxl/mem: Implement Clear Event Records command

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Date:   Fri, 2 Dec 2022 13:18:36 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Dan Williams <dan.j.williams@...el.com>
CC:     <ira.weiny@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Dave Jiang <dave.jiang@...el.com>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>
Subject: Re: [PATCH V2 03/11] cxl/mem: Implement Clear Event Records command


> > +static int cxl_clear_event_record(struct cxl_dev_state *cxlds,
> > +				  enum cxl_event_log_type log,
> > +				  struct cxl_get_event_payload *get_pl,
> > +				  u16 total)
> > +{
> > +	struct cxl_mbox_clear_event_payload payload = {
> > +		.event_log = log,
> > +	};
> > +	int cnt;
> > +
> > +	/*
> > +	 * Clear Event Records uses u8 for the handle cnt while Get Event
> > +	 * Record can return up to 0xffff records.
> > +	 */
> > +	for (cnt = 0; cnt < total; /* cnt incremented internally */) {
> > +		u8 nr_recs = min_t(u8, (total - cnt),
> > +				   CXL_CLEAR_EVENT_MAX_HANDLES);  
> 
> This seems overly complicated. @total is a duplicate of
> @get_pl->record_count, and the 2 loops feel like it could be cut
> down to one.


You could do something nasty like
	for (i = 0; i < total; i++) {

		...
		payload.handle[i % CLEAR_EVENT_MAX_HANDLES] = ...
		if (i % CXL_CLEAR_EVENT_MAX_HANDLES == CXL_CLEAR_EVENT_MAX_HANDLE - 1) {
			send command.
		}
	}

but that looks worse to me than the double loop.

Making outer loop
	for (j = 0; j <= total / CXL_CLEAR_EVENT_MAX_HANDLES; j++)
might bet clearer but then you'd have to do
records[j * CXL_CLEAR_EVENT_MAX_HANDLES + i] which isn't nice.

Ah well, Ira gets to try and find a happy compromise.


...

> > diff --git a/include/uapi/linux/cxl_mem.h b/include/uapi/linux/cxl_mem.h
> > index 70459be5bdd4..7c1ad8062792 100644
> > --- a/include/uapi/linux/cxl_mem.h
> > +++ b/include/uapi/linux/cxl_mem.h
> > @@ -25,6 +25,7 @@
> >  	___C(RAW, "Raw device command"),                                  \
> >  	___C(GET_SUPPORTED_LOGS, "Get Supported Logs"),                   \
> >  	___C(GET_EVENT_RECORD, "Get Event Record"),                       \
> > +	___C(CLEAR_EVENT_RECORD, "Clear Event Record"),                   \
> >  	___C(GET_FW_INFO, "Get FW Info"),                                 \
> >  	___C(GET_PARTITION_INFO, "Get Partition Information"),            \
> >  	___C(GET_LSA, "Get Label Storage Area"),                          \  
> 
> Same, "yikes" / "must be at the end of the enum" feedback.

Macro magic makes that non obvious.. Not that I'd ever said I thought this trick
was a bad idea ;)