From b0876afdff45a4714e11f18ebbfb81762b417eac Mon Sep 17 00:00:00 2001 From: Dave Gordon Date: Wed, 14 Sep 2016 13:10:33 +0100 Subject: [PATCH] drm/i915: Only expand COND once in wait_for() 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 1410fd before > 1305341 5184 1152 1311677 1403bd 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 Original-idea-by: Chris Wilson Cc: Chris Wilson Cc: Zanoni, Paulo R Link: http://patchwork.freedesktop.org/patch/msgid/1473855033-26980-1-git-send-email-david.s.gordon@intel.com Reviewed-by: Paulo Zanoni Signed-off-by: Chris Wilson --- 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 7700e3254b26..810c89eb6863 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()) { \ -- 2.20.1