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

From: Joe Perches
Date: Thu Feb 28 2008 - 20:14:20 EST


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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