linux-kernel - Re: [PATCH] linux/fs.h - Convert debug functions declared inline __attribute__((format (printf,x,y) to statement expression macros

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Message-Id: <1204247347.9959.31.camel@localhost>
Date:	Thu, 28 Feb 2008 17:09:07 -0800
From:	Joe Perches <joe@...ches.com>
To:	Jan Hubicka <hubicka@....cz>
Cc:	Jakub Jelinek <jakub@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Matthew Wilcox <matthew@....cx>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, gcc@....gnu.org,
	zadeck@...uralbridge.com
Subject: Re: [PATCH] linux/fs.h - Convert debug functions declared inline 
	__attribute__((format (printf,x,y) to statement expression macros

On Thu, 2008-02-28 at 11:23 +0100, Jan Hubicka wrote:
> The call ought to be always
> early inlined and not seen by any optimization pass.

The inlined functions don't actually appear in the generated code.

Look at the code generation differences for kernel/sched.c
function place_entity

$ size sched.inline.o sched.if0.o
   text    data     bss     dec     hex filename
  31385    2854     328   34567    8707 sched.inline.o
  31366    2854     328   34548    86f4 sched.if0.o

The current preprocessed only kernel/sched.i file contains:

# 612 "include/linux/device.h"
static inline __attribute__((always_inline)) int __attribute__ ((format (printf, 2, 3)))
dev_dbg(struct device *dev, const char *fmt, ...)
{
 return 0;
}
# 628 "include/linux/device.h"
static inline __attribute__((always_inline)) int __attribute__ ((format (printf, 2, 3)))
dev_vdbg(struct device *dev, const char *fmt, ...)
{
 return 0;
}

But the function place_entity doesn't use it directly or indirectly.
If the lines above are removed, the generated code for place_entity changes.

static void
place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
{
	u64 vruntime;

	vruntime = cfs_rq->min_vruntime;

	if (sched_feat(TREE_AVG)) {
		struct sched_entity *last = __pick_last_entity(cfs_rq);
		if (last) {
			vruntime += last->vruntime;
			vruntime >>= 1;
		}
	} else if (sched_feat(APPROX_AVG) && cfs_rq->nr_running)
		vruntime += sched_vslice(cfs_rq)/2;

	/*
	 * The 'current' period is already promised to the current tasks,
	 * however the extra weight of the new task will slow them down a
	 * little, place the new task so that it fits in the slot that
	 * stays open at the end.
	 */
	if (initial && sched_feat(START_DEBIT))
		vruntime += sched_vslice_add(cfs_rq, se);

	if (!initial) {
		/* sleeps upto a single latency don't count. */
		if (sched_feat(NEW_FAIR_SLEEPERS))
			vruntime -= sysctl_sched_latency;

		/* ensure we never gain time by being placed backwards. */
		vruntime = max_vruntime(se->vruntime, vruntime);
	}

	se->vruntime = vruntime;
}


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