Em Qua, 2016-09-14 às 13:10 +0100, Dave Gordon escreveu:
> Commentary from Chris Wilson's original version:
>
> >
> > I was looking at some wait_for() timeouts on a slow system, with
> > lots of
> > debug enabled (KASAN, lockdep, mmio_debug). Thinking that we were
> > mishandling the timeout, I tried to ensure that we loop at least
> > once
> > after first testing COND. However, the double test of COND either
> > side
> > of the timeout check makes that unlikely. But we can do an
> > equivalent
> > loop, that keeps the COND check after testing for timeout (required
> > so
> > that we are not preempted between testing COND and then testing for
> > a
> > timeout) without expanding COND twice.
> >
> > The advantage of only expanding COND once is a dramatic reduction
> > in
> > code size:
> >
> > text data bss dec hex
> > 1308733 5184 1152 1315069 141
> > 0fd before
> > 1305341 5184 1152 1311677 140
> > 3bd after
>
> but it turned out that due to a missing iniitialiser, gcc had "gone
> wild trimming undefined code" :( This version acheives a rather more
> modest (but still worthwhile) gain of ~550 bytes.
>
> Signed-off-by: Dave Gordon <david.s.gordon@xxxxxxxxx>
> Original-idea-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Zanoni, Paulo R <paulo.r.zanoni@xxxxxxxxx>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_drv.h | 14 +++++++++-----
> 1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_drv.h
> b/drivers/gpu/drm/i915/intel_drv.h
> index abe7a4d..8fd16ad 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -52,11 +52,15 @@
> */
> #define _wait_for(COND, US, W) ({ \
> unsigned long timeout__ = jiffies + usecs_to_jiffies(US) +
> 1; \
> - int ret__ = 0;
> \
> - while (!(COND)) {
> \
> - if (time_after(jiffies, timeout__)) {
> \
> - if (!(COND))
> \
> - ret__ = -ETIMEDOUT;
> \
> + int ret__;
> \
> + for (;;) {
> \
> + bool expired__ = time_after(jiffies, timeout__);
> \
> + if (COND) {
> \
> + ret__ = 0;
> \
> + break;
> \
> + }
> \
> + if (expired__) {
> \
> + ret__ = -ETIMEDOUT;
> \
> break;
> \
> }
> \
> if ((W) && drm_can_sleep()) {
> \
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